Microbiology Flashcards
- Sputum culture
A 24 year-old Asian man presents with a persistent cough. A sputum sample is taken and cultured on Lowenstein–Jensen medium, appearing as brown, granular colonies after several weeks. The organism implicated is:
A Coxiella burnetti B Streptococcus pneumoniae C Mycobacterium tuberculosis D Legionella pneumophilia E Mycobacterium leprae
C
Mycobacterium tuberculosis which characteristically presents with a persistent cough, haemoptysis, fever, night sweats and weight loss. Lowenstein–Jensen medium is a growth medium used to culture Mycobacterium species at 37°C. The most common indication for its use is to culture Mycobacterium tuberculosis (C), where it appears as brown coffee-coloured (buff), granular bread crumb-like colonies (rough) which often stick to the bottom of the growth plate and are hard to remove (tough). Remembered as ‘buff, rough and tough’. It usually takes ~4–6 weeks to obtain these visible colonies, an important fact to remember when treating patients. Another characteristic feature is the formation of serpentine rods from chains of cells in smears. They are classified as acid-fast bacteria, because they are resistant to losing their colour during staining procedures. The Ziehl–Neelson stain used to stain this type of bacterium - appear bright red against a blue background. The stain contains carbofuchsin, a pink dye which binds to the unique mycolic acids found in the mycobacterium cell wall. Another stain used for acid-fast bacilli is auramine, which also binds to mycolic acids to give a yellow fluorescence.
Mycobacterium leprae (E) is another acid-fast bacillus, responsible for causing leprosy. It can be detected using skin biopsy or nasal smear, using Fite stain. It has proven difficult to culture on artificial cell media, but instead has been grown on mouse foot pads and nine-banded armadillos. Symptoms of leprosy include hypopigmented skin lesions, nodules and loss of sensation.
Coxiella burnetii (A) causes Q fever, which was first described in abbatoir workers. It is an obligate intracellular Gram-negative bacte- rium found in farm animals and pets, and is transmitted by aerosol or contact with animal products like milk or faeces. It manifests as flu-like symptoms, but can progress to an atypical pneumonia or less often a granulomatous hepatitis. Typical chest X-ray features include a ground glass appearance. It does not grow on Lowenstein–Jensen medium.
Streptococcus pneumoniae (B) is a Gram-positive coccus causing a lobar pneumonia, and can be differentiated from Streptococcus viridans using an optochin test. Streptococcus pneumoniae and viridans are alpha haemolytic, but Strep. pneumoniae are optochin sensitive whilst Strep. viridans are optochin resistant. It also does not grow on Lowenstein–Jensen medium.
Legionella pneumophilia (D) is a Gram-negative bacterium that causes Legionnaire’s disease. It typically presents initially with flu-like symptoms, progressing to a productive cough and sometimes diarrhoea and confusion due to hyponatraemia. It can be detected using a urinary antigen test, or by culture on buffered charcoal yeast extract, but not Lowenstein–Jensen medium.
- Mantoux test
A 24-year-old HIV-positive Asian man presents with a cough. A Mantoux test is performed. After 72 hours, the wheal diameter is measured at 5.8mm. This indicates:
A He has never been exposed to TB
B He has been exposed to TB
C He has had a BCG vaccination in the past
D He has latent TB which is now reactivated
E It is not possible to say
B
The Mantoux test is a diagnostic test for tuberculosis. It consists of an intradermal injection of 0.1mL of purified protein derivative (PPD) tuberculin, which is a glycerol extract of the bacillus. The diameter of the induration that subsequently forms is read 48–72 hours later, but one also needs to take into account the patient’s risk of being infected with TB and of progression to disease if they were infected in interpreting the result. The Centers for Disease Control and Prevention provide the following classification for the skin test:
1) An induration of 5 mm or more is considered positive in:
- Patients with HIV
- A recent contact of a person with TB disease
- People with fibrotic changes on CXR consistent with prior TB
- Patients with organ transplants
- People who are immunosuppressed for other reasons (eg. taking the equivalent of >15mg/day of prednisone for 1 month or longer)
2) An induration of 10 mm or more is considered positive in:
- Recent immigrants (<5 years) from high-prevalence countries
- IVDUs
- Residents and employees of high-risk congregate settings
- Mycobacteriology laboratory personnel
- Persons with clinical conditions that place them at high risk
- Children <4 years of age
- Infants, children, & adolescents exposed to adults in high-risk categories
3) An induration of 15 mm or more is considered positive in any person, including those with no known risk factors for TB
So for the patient in the question, a lower cut off is used to interpret the test as he has HIV. The reasoning behind this is that as he is likely to have a depleted CD4 T-cell count, which are the cells involved in mounting a type IV sensitivity reaction to the injection to produce a positive result; if we were to use the normal cut off of 15mm there is a chance we would obtain a false negative result for him. A positive result indicates that the person has been exposed to TB (B), which could include previous BCG exposure (C). Whilst (C) could also be correct, the single best answer in this case is (B) as this encompasses both pos- sibilities.
Answers (A) and (E) are clearly not correct, as using the above guidelines the result is positive for an HIV patient.
Answer (D) could again be possible but it may also be true that his infected state is a result of a de novo infection, and not a reactivation of latent TB.
- Pneumonia (1)
An 18-year-old university student develops a lower lobe pneumonia, with a raised white cell count and CRP. A sputum culture reveals a Gram-positive optochin-sensitive diplococcus. The most likely causative agent is:
A Staphylococcus aureus B Streptococcus viridans C Mycoplasma pneumoniae D Streptococcus pneumoniae E Haemophilus influenzae
D
It is useful to remember that streptococci can essentially be divided into alpha haemolytic, beta haemolytic and non-haemolytic groups. Alpha haemolytic streptococci can be further divided into Strep. pneumoniae (D) and Strep. viridans (B) according to their optochin sensitivity (amongst other factors). The beta haemolytic streptococci are further classified according to Lancefield groups A, B, C, F and G. Finally the non-haemolytic streptococci include the enterococci. Optochin is an antibiotic used to differentiate Strep. pneumoniae from other alpha haemolytic streptococci such as Strep. viridans. The pneumococcus will typically produce a zone of inhibition around an optochin disc, indicating that it is sensitive to the antibiotic, whereas Strep. viridans is resistant to it so its growth will not be affected. This can be remembered using the mnemonic ‘OVeR PS’ (Optochin – Viridans Resistant, Pneumococci Sensitive). As the organism in the question is optochin sensitive, the answer is (D).
Staphylococcus aureus would not be optochin sensitive, so (A) is not the correct answer. It is a Gram-positive bacterium that obtained its name because of the golden yellow colonies that form when grown on blood agar plates (aurum is Latin for gold).
Mycoplasma pneumoniae (C) generally causes an atypical pneumonia in children and young adults. It is called the ‘walking pneumonia’ because patients can sometimes continue walking around despite suffering from it, and many are asymptomatic. The clinical features of this pneumonia can on occasion be relatively insignificant compared to the radiological findings. It too is not optochin sensitive so is not the correct answer here.
Haemophilus influenzae (E) is a Gram-negative bacillus so can be easily eliminated as a potentially correct answer here. Clinically the pneumonia caused by Haemophilus is not easily distinguished from that caused by Strep. pneumoniae.
- Pneumonia (2)
A 58-year-old Caucasian alcoholic man presents to his GP with a history of sudden onset high fever, flu-like symptoms and, thick, blood stained sputum.
A chest X-ray is arranged which shows marked upper lobe cavitation. The most likely causative agent is:
A Klebsiella pneumoniae B Mycobacterium tuberculosis C Staphylococcus aureus D Moraxella catarrhalis E Pnemocystis jirovecii
A
Klebsiella pneumoniae (A) is a Gram-negative rod-shaped bacillus that can cause an atypical pneumonia, most frequently in alcoholics. It can result in sudden, severe systemic upset in these patients, and the pro- duction of thick, purulent and sometimes blood-stained sputum said to resemble ‘red-currant jelly’. Haemoptysis occurs more frequently with K. pneumoniae than with pneumonia caused by other bacteria. Radiological features can include upper lobe consolidation, with marked cavitation as described in the question. It is more likely to lead to complications such as lung abscesses and empyemas than pneumonias caused by Strep. pneumoniae.
Mycobacterium tuberculosis (B) can cause haemoptysis and upper lobe cavitation. Whilst a plausible answer, the indication that the patient is alcoholic, coupled with the characteristic description of thick, blood-stained sputum, is more characteristic of Klebsiella. Also note the absence of other typical indicators of tuberculosis such as night sweats, weight loss and Asian ethnicity.
Pneumonia caused by Staphyloccous aureus (C) can follow an influenza virus infection, and may result in the formation of abscesses. The radiological findings can include extensive cavitation, and thin walled abscesses may break down to give a cystic appearance. Whilst S. aureus could potentially lead to the above clinical picture, Klebsiella is again more likely to give blood-stained sputum in an alcoholic.
Moraxella catarrhalis (D) is a Gram-negative diplococcus that may cause pneumonia in patients with underlying lung disease such as chronic obstructive pulmonary disease (COPD). It can be implicated in an infective exacerbation of their condition in these patients. It can also lead to laryngitis, otitis media and sinusitis. Given the presumed absence of an underlying lung condition in this patient, it is less likely to be the causative agent than Klebsiella.
Pneumocystis jirovecii (E) tends to affect immunocompromised patients, and used to be called pneumocystis pneumonia (PCP). Typical clinical features include severe shortness of breath, dry cough and the presence of bilateral crackles. If you get an HIV patient whose saturations drop on exertion in a question, think about this organism! It does not normally give bilateral cavitation on a chest X-ray, but instead would characteristically show peri-hilar interstitial infiltrates, giving a ‘bat’s wing’ appearance. Histology may reveal classic boat-shaped organisms, and the diagnostic stain used is the silver stain.
- Endocarditis
A 27-year-old intravenous drug user presents with a 2-week history of fevers, weight loss and a systolic murmur. The most likely causative agent is:
A Streptococcus viridans B Candida albicans C Staphylococcus aureus D Streptococcus bovis E Kingella
C
Infective endocarditis can be classified into two broad categories: acute and sub-acute. Acute infective endocarditis is less common, and the most likely causative agent is Staphylococcus aureus (C). It can affect both normal and abnormal valves, and can typically be found in intravenous drug users, such as the patient described. The tricuspid valve is most commonly affected in these cases, which can easily be remembered as this is the first valve that the bacteria will encounter following injection into a vein. Therefore, (C) is the correct answer in this case.
The other category of infective endocarditis is the sub-acute form, which is more common. It is most often caused by Streptococcus viridans (A), and usually occurs on damaged valves. Patients typically present with an insidious onset of fevers, night sweats, and weight loss. Other clinical features can result from emboli, such as cerebral emboli causing a stroke, or less commonly recurrent pulmonary emboli in right sided endocarditis. If asked about the signs of endocarditis, steer away from mentioning the rare eponymous signs first! You can remember the signs as rules of two: two signs in the hands include clubbing and splinter haemorrhages, two signs in the abdomen are splenomegaly and microscopic haematuria, and two signs elsewhere can include new or changing heart murmurs and embolic phenomena. Remember that the most common valves to be affected are the aortic and mitral valves.
Fungi such as Candida albicans (B) are a much less common cause of endocarditis. They can also be found in intravenous drug users, but this is much less likely than Staphylococcus aureus. They can include Aspergillus and Candida species, and usually cause a sub-acute picture.
Strep. bovis (D) has also been implicated as a rarer cause of infective endocarditis, and is part of the natural flora of the bowel. If found in a patient with endocarditis, a colonoscopy may be important as its presence is associated with colonic malignancies.
The HACEK organisms consist of a Gram-negative group which includes Haemophilus parainfluenzae, Aggregatibacter, Cardiobacterium hominis, Eikenella corrodens and Kingella (E). They typically result in a culture negative endocarditis. Whilst all of the above answers are possible, the single best answer is Staphylococcus aureus because the patient is an intravenous drug user and has developed an acute form of the disease.
Zoonoses
A Psittacosis B Rabies C Brucellosis D Q fever E Leptospirosis F Mycobacterium marinium G Lyme disease H Cat scratch disease I Rocky mountain spotted fever
1 A 45-year-old man has returned to the UK from a holiday to France. A week later he presents with flu-like symptoms, drenching sweats, a recurring fever and is beginning to complain of a lower back pain. He admits to have brought back some local cheeses on visits to regional farms.
1)C
Brucellosis (C) is a Gram-negative rod-shaped bacterium that is harboured by cattle (Brucella abortus), goats (B. melitensis), pigs (B. suis) and dogs (B. canis). Brucella spp. are transmitted by inhalation, unpasteurized dairy produce and direct contact with animals. Symptoms include fever, myalgia, arthralgia, tiredness and in chronic cases may be associated with depression. Diagnosis by blood culture on Castaneda medium. Complications = granulomatous hepatitis (histology of liver biopsy demonstrates granulomata), endocarditis, oseteomyelitis and thrombocytopenia.
Rabies (B) is a viral zoonotic infectious disease caused by a bite or scratch, usually from an infected dog or bat. Infection leads to progressive and incurable encephalitis, hydrophobia and muscle spasm. Cerebral Negri bodies (inclusion bodies) are pathognomonic.
Q fever (D) is caused by Coxiella burnetti. Transmission occurs by inhalation of aerosols of urine, faeces or amniotic fluid from infected livestock.
Mycobacterium marinium (F) is harboured by fish and is transmitted by a bite or injury from the fin. Infection causes nodules to appear on the elbows, knees and feet.
Cat scratch disease (H) is caused by Bartonella spp. bacteria transmitted by bites from cats. Classically, infection results in tender and swollen lymph nodes with headache and backache. Atypically, infection may result in Parinaud’s oculoglandular syndrome.
Zoonoses
A Psittacosis B Rabies C Brucellosis D Q fever E Leptospirosis F Mycobacterium marinium G Lyme disease H Cat scratch disease I Rocky mountain spotted fever
2 A 36-year-old man presents to his GP with a painful right knee. He states that he visited the Prairie regions of Canada a month previous to this episode and states that his wife had mentioned there was a red rash on his back; on examination a target shaped rash is observed.
2)G
Lyme disease (G) is caused by the spirochaete Borrelia burgdorferi which is transmitted by the Ixodes ticks harboured by certain species of mice and deer. Initial symptoms include erythema migrans (a spreading annular skin lesion with a characteristic target-shaped appearance), malaise, fever and musculoskeletal pain. Several weeks after the primary infection, the patient may experience neurological (headache, meningitis and Bell’s palsy) and cardiac (arrhythmias, myocarditis and pericarditis) effects. Late features include arthralgia and arthritis.
Rabies (B) is a viral zoonotic infectious disease caused by a bite or scratch, usually from an infected dog or bat. Infection leads to progressive and incurable encephalitis, hydrophobia and muscle spasm. Cerebral Negri bodies (inclusion bodies) are pathognomonic.
Q fever (D) is caused by Coxiella burnetti. Transmission occurs by inhalation of aerosols of urine, faeces or amniotic fluid from infected livestock.
Mycobacterium marinium (F) is harboured by fish and is transmitted by a bite or injury from the fin. Infection causes nodules to appear on the elbows, knees and feet.
Cat scratch disease (H) is caused by Bartonella spp. bacteria transmitted by bites from cats. Classically, infection results in tender and swollen lymph nodes with headache and backache. Atypically, infection may result in Parinaud’s oculoglandular syndrome.
Zoonoses
A Psittacosis B Rabies C Brucellosis D Q fever E Leptospirosis F Mycobacterium marinium G Lyme disease H Cat scratch disease I Rocky mountain spotted fever
3 A 38-year-old sewage worker presents to his GP with 1-week history of flu-like symptoms with diarrhoea. A microscopic agglutination test reveals the diagnosis.
3)E
Leptospirosis (Weil’s disease; E) is a zoonotic disease caused by Leptospira interrogans which is harboured by both wild and domestic animals. It is transmitted via drinking water that has become contaminated with the urine of infected animals; as a result those involved in water-sports and sewage workers are at particular risk. Lyme disease is characterized by an influenza-like disease with/without gastrointestinal symptoms. Diagnosis can be made by ELISA, PCR or microscopic agglutination test (MAT). Long-term complications include hepatitis and renal failure.
Rabies (B) is a viral zoonotic infectious disease caused by a bite or scratch, usually from an infected dog or bat. Infection leads to progressive and incurable encephalitis, hydrophobia and muscle spasm. Cerebral Negri bodies (inclusion bodies) are pathognomonic.
Q fever (D) is caused by Coxiella burnetti. Transmission occurs by inhalation of aerosols of urine, faeces or amniotic fluid from infected livestock.
Mycobacterium marinium (F) is harboured by fish and is transmitted by a bite or injury from the fin. Infection causes nodules to appear on the elbows, knees and feet.
Cat scratch disease (H) is caused by Bartonella spp. bacteria transmitted by bites from cats. Classically, infection results in tender and swollen lymph nodes with headache and backache. Atypically, infection may result in Parinaud’s oculoglandular syndrome.
Zoonoses
A Psittacosis B Rabies C Brucellosis D Q fever E Leptospirosis F Mycobacterium marinium G Lyme disease H Cat scratch disease I Rocky mountain spotted fever
4 A 48-year-old man presents to his GP with flu-like symptoms. On examination the patient has a maculopapular rash on his trunk. The patient also shows an area where a vague bite mark is visible.
4)I
Rocky Mountain spotted fever (I) is caused by Rickettsia spp. infection, a Gram-negative genus of bacteria, most prevalent in North and South America. It is harboured in small wild rodents and domestic animals (transmitted to humans by ticks). Rickettsia bacteria invade the endothe- lial lining of capillaries causing a vasculitis. Clinical features include headache, fever, myalgia, vomiting and confusion. Late signs include a rash that is maculopapular and/or petechial on the distal parts of the limbs which then spreads to the trunk and face. Rocky Mountain spotted fever may lead to thrombocytopenia, hyponatraemia and/or elevated liver enzymes.
Rabies (B) is a viral zoonotic infectious disease caused by a bite or scratch, usually from an infected dog or bat. Infection leads to progressive and incurable encephalitis, hydrophobia and muscle spasm. Cerebral Negri bodies (inclusion bodies) are pathognomonic.
Q fever (D) is caused by Coxiella burnetti. Transmission occurs by inhalation of aerosols of urine, faeces or amniotic fluid from infected livestock.
Mycobacterium marinium (F) is harboured by fish and is transmitted by a bite or injury from the fin. Infection causes nodules to appear on the elbows, knees and feet.
Cat scratch disease (H) is caused by Bartonella spp. bacteria transmitted by bites from cats. Classically, infection results in tender and swollen lymph nodes with headache and backache. Atypically, infection may result in Parinaud’s oculoglandular syndrome.
Zoonoses
A Psittacosis B Rabies C Brucellosis D Q fever E Leptospirosis F Mycobacterium marinium G Lyme disease H Cat scratch disease I Rocky mountain spotted fever
2 A 36-year-old man presents to his GP with a painful right knee. He states that he visited the Prairie regions of Canada a month previous to this episode and states that his wife had mentioned there was a red rash on his back; on examination a target shaped rash is observed.
2)G
Lyme disease (G) is caused by the spirochaete Borrelia burgdorferi which is transmitted by the Ixodes ticks harboured by certain species of mice and deer. Initial symptoms include erythema migrans (a spreading annular skin lesion with a characteristic target-shaped appearance), malaise, fever and musculoskeletal pain. Several weeks after the primary infection, the patient may experience neurological (headache, meningitis and Bell’s palsy) and cardiac (arrhythmias, myocarditis and pericarditis) effects. Late features include arthralgia and arthritis.
Rabies (B) is a viral zoonotic infectious disease caused by a bite or scratch, usually from an infected dog or bat. Infection leads to progressive and incurable encephalitis, hydrophobia and muscle spasm. Cerebral Negri bodies (inclusion bodies) are pathognomonic.
Q fever (D) is caused by Coxiella burnetti. Transmission occurs by inhalation of aerosols of urine, faeces or amniotic fluid from infected livestock.
Mycobacterium marinium (F) is harboured by fish and is transmitted by a bite or injury from the fin. Infection causes nodules to appear on the elbows, knees and feet.
Cat scratch disease (H) is caused by Bartonella spp. bacteria transmitted by bites from cats. Classically, infection results in tender and swollen lymph nodes with headache and backache. Atypically, infection may result in Parinaud’s oculoglandular syndrome.
Sexually transmitted infections
A Treponema pallidum B Klebsiella granulomatis C Neiserria gonorrhoeae D Trichomonas vaginalis E Candidia albicans F Chlamydia trachomatis G Bacterial vaginosis H Haemophilus ducreyi I Herpes simplex virus 2
1 A 28-year-old woman sees her GP complaining of fever, lower abdominal pain and painful intercourse. Vaginal swabs are sent for a nucleic acid amplification test which reveal sexually transmitted bacteria that can also cause lymphogranuloma venereum.
1)F
Chlamydia trachomatis (F) is a small Gram-negative obligate intracellular bacterium, causing the sexually transmitted infection chlamydiosis. It has an affinity towards columnar epithelia that line mucous membranes. Serovars D–K cause genital chlamydiosis (as well as opthalmia neonatorum) resulting in dyspareunia, dysuria and vaginal/penile discharge. Serovars L1, L2 and L3 cause lymphogranuloma venereum, defined by a painless papule or ulcer on the genitals which heals spontaneously; the bacteria migrate along regional lymph nodes leading to lymphadenopathy.
Klebsiella granulomatis (B) is a Gram-positive rod that causes the ulcerating sexually transmitted infection donovanosis. It is diagnosed using giemsa stain of biopsy, which reveals Donovan bodies.
Trichomonas vaginalis (D) is a flagellated protozoan that causes vaginal discharge and urethritis in humans. It is otherwise asymptomatic and can be diagnosed by wet preparation microscopy, culture or PCR.
Candida albicans (E) is a fungal infection that causes candidiasis (thrush). Superficially, infection causes redness, itching and discharge from the vagina. In immunocompromised patients, infection can involve the oesophagus as well as causing candidaemia.
Herpes simplex virus 2 (HSV-2; I) causes genital herpes. Infection causes fluid-filled blisters to form over the genital area.
Sexually transmitted infections
A Treponema pallidum B Klebsiella granulomatis C Neiserria gonorrhoeae D Trichomonas vaginalis E Candidia albicans F Chlamydia trachomatis G Bacterial vaginosis H Haemophilus ducreyi I Herpes simplex virus 2
2 A 68-year-old man presents to his GP with a gumma on his nose. On examination, the patient is found to have pupils that accommodate to light but do not react. The man admits to unprotected sexual intercourse during his youth.
2)A
Treponema pallidum (A) causes syphilis. Syphilis has 3 clinical stages: 1o, 2o and 3o. Primary syphilis is defined by a firm painless chancre that appears approximately 1 month after sexual contact and resolves within a few weeks. 2o syphilis is a bacteriaemic stage during which a widespread rash forms with lymphadenopathy. 3o syphilis occurs decades after the primary infection and involves multiple organs: gummatous lesions on skin and bone, aneurysm of the aortic arch, peripheral neuropathy, tabes dorsalis and Argyll–Robertson pupils.
Klebsiella granulomatis (B) is a Gram-positive rod that causes the ulcerating sexually transmitted infection donovanosis. It is diagnosed using giemsa stain of biopsy, which reveals Donovan bodies.
Trichomonas vaginalis (D) is a flagellated protozoan that causes vaginal discharge and urethritis in humans. It is otherwise asymptomatic and can be diagnosed by wet preparation microscopy, culture or PCR.
Candida albicans (E) is a fungal infection that causes candidiasis (thrush). Superficially, infection causes redness, itching and discharge from the vagina. In immunocompromised patients, infection can involve the oesophagus as well as causing candidaemia.
Herpes simplex virus 2 (HSV-2; I) causes genital herpes. Infection causes fluid-filled blisters to form over the genital area.
Sexually transmitted infections
A Treponema pallidum B Klebsiella granulomatis C Neiserria gonorrhoeae D Trichomonas vaginalis E Candidia albicans F Chlamydia trachomatis G Bacterial vaginosis H Haemophilus ducreyi I Herpes simplex virus 2
3 A 35-year-old man presents to an infectious disease specialist with a painful penile ulcer and associated unilateral lymphadenopathy of the inguinal nodes. A swab of the ulcer is cultured on chocolate agar.
3)H
Haemophilus ducreyi (H) is a Gram-negative coccobacillus that causes a tropical ulcer disease (chancroid) and is contracted by sexual transmission. Chancroid is characterized by a painful genital ulcer that leads to unilateral painful swollen inguinal lymph nodes. Infected lymph nodes may rupture releasing pus. The differential diagnosis for genital ulcers includes syphilis (painless ulcer with bilateral painless lymphadenopathy), herpes simplex virus 1 and 2 (vesicles that eventually break down) and lymphogranuloma venereum (slowly developing painless inguinal lymph nodes). Haemophilus ducreyi can be cultured on chocolate agar.
Klebsiella granulomatis (B) is a Gram-positive rod that causes the ulcerating sexually transmitted infection donovanosis. It is diagnosed using giemsa stain of biopsy, which reveals Donovan bodies.
Trichomonas vaginalis (D) is a flagellated protozoan that causes vaginal discharge and urethritis in humans. It is otherwise asymptomatic and can be diagnosed by wet preparation microscopy, culture or PCR.
Candida albicans (E) is a fungal infection that causes candidiasis (thrush). Superficially, infection causes redness, itching and discharge from the vagina. In immunocompromised patients, infection can involve the oesophagus as well as causing candidaemia.
Herpes simplex virus 2 (HSV-2; I) causes genital herpes. Infection causes fluid-filled blisters to form over the genital area.
Sexually transmitted infections
A Treponema pallidum B Klebsiella granulomatis C Neiserria gonorrhoeae D Trichomonas vaginalis E Candidia albicans F Chlamydia trachomatis G Bacterial vaginosis H Haemophilus ducreyi I Herpes simplex virus 2
4 A 28-year-old woman sees her GP complaining of fever, lower abdominal pain and painful intercourse. A vaginal swab is taken and subsequent Gram-staining reveals Gram-negative diplococci.
4)C
Neiserria gonorrhoeae (gonococcus; C) is an intracellular Gram-negative diplococcus that causes gonorrhoea. Virulence factors allow gonococci to evade phagocytosis and adhere to the non-ciliated epithelium of the fallopian tubes. In both men and women N. gonorrhoeae causes urethritis which presents with dysuria and purulent discharge (with associated dyspareunia in women). Long-term complications include PID in women and epididymitis, prostititis & urethral stricture in men. Systemic invasion of bacteria causes pericarditis, endocarditis, meningitis and/or septic arthritis. Diagnosis involves Gram stain and culture on Thayer–Martin VCN medium, or PCR.
Klebsiella granulomatis (B) is a Gram-positive rod that causes the ulcerating sexually transmitted infection donovanosis. It is diagnosed using giemsa stain of biopsy, which reveals Donovan bodies.
Trichomonas vaginalis (D) is a flagellated protozoan that causes vaginal discharge and urethritis in humans. It is otherwise asymptomatic and can be diagnosed by wet preparation microscopy, culture or PCR.
Candida albicans (E) is a fungal infection that causes candidiasis (thrush). Superficially, infection causes redness, itching and discharge from the vagina. In immunocompromised patients, infection can involve the oesophagus as well as causing candidaemia.
Herpes simplex virus 2 (HSV-2; I) causes genital herpes. Infection causes fluid-filled blisters to form over the genital area.
Sexually transmitted infections
A Treponema pallidum B Klebsiella granulomatis C Neiserria gonorrhoeae D Trichomonas vaginalis E Candidia albicans F Chlamydia trachomatis G Bacterial vaginosis H Haemophilus ducreyi I Herpes simplex virus 2
5 A 35-year-old woman presents to her GP with a 2-week history of a fishy odorous vaginal discharge, which occurs especially after sexual intercourse. Microscopy of the discharge reveals clue cells.
5)G
Bacterial vaginosis (BV; G) is caused by an imbalance in the naturally occurring bacterial flora of the vagina and is a condition associated with sexual activity (not transmitted). A ‘fishy’ smelling white–cream vaginal discharge is characteristically produced. Diagnosis with vaginal swabs. A litmus test will indicate loss of acidity with a pH greater than 4.5 (normal vaginal pH = 3.8–4.2). If a sample of the discharge is visualized under a microscope with sodium chloride, clue cells will be seen.
Klebsiella granulomatis (B) is a Gram-positive rod that causes the ulcerating sexually transmitted infection donovanosis. It is diagnosed using giemsa stain of biopsy, which reveals Donovan bodies.
Trichomonas vaginalis (D) is a flagellated protozoan that causes vaginal discharge and urethritis in humans. It is otherwise asymptomatic and can be diagnosed by wet preparation microscopy, culture or PCR.
Candida albicans (E) is a fungal infection that causes candidiasis (thrush). Superficially, infection causes redness, itching and discharge from the vagina. In immunocompromised patients, infection can involve the oesophagus as well as causing candidaemia.
Herpes simplex virus 2 (HSV-2; I) causes genital herpes. Infection causes fluid-filled blisters to form over the genital area.
Respiratory tract infections
A Streptococcus pneumoniae B Moraxella catarrhalis C Haemophilus influenzae D Legionella pneumophila E Mycoplasma pneumonia F Chlamydia pneumoniae G Mycobacterium tuberculosis H Pneumocystis jirovecii I Staphylococcus aureus
1 A 25-year-old man with a history of recurrent chest infections presents to an infectious disease specialist. A subsequent chest X-ray demonstrates widespread pulmonary infiltrates. A sputum stain using Gomori’s methenamine silver reveals characteristic cysts.
1) H
Pneumocystis jirovecii (H) is a yeast-like fungus that primarily affects immunocompromised patients such as those with HIV. Pneumocystis pneumonia may be the presenting feature of HIV and patients with a CD4 count less than 200cells/μL are particularly susceptible. Clinically, Pneumocystis jirovecii infection presents with fever, non-productive cough, weight loss and night sweats. Chest X-ray may show signs of diffuse bilateral pulmonary infiltrates. Definitive diagnosis involves histological examination of sputum or bronchio-alveolar lavage fluid. Gomori’s methenamine silver stain reveals ‘flying saucer’ shaped cysts on microscopy.
Moraxella catarrhalis (B) are aerobic Gram-negative diploccoci. This bacterium is particularly problematic in patients with chronic lung disease and causes exacerbations of chronic obstructive pulmonary disorder (COPD). Other targets of infection include ears, eyes and central nervous system.
Haemophilus influenzae (C) are Gram-negative bacilli that cause influenza (flu) outbreaks annually. Chocolate agar is used as a culture medium. Further oxidase and catalase tests are positive.
Mycoplasma pneumoniae (E) are obligate intracellular bacteria which cause an atypical pneumonia or a mild bronchitis. A cold-agglutinin test can be used for the diagnosis. In rare cases, infection may lead to Stevenson–Johnson syndrome.
Chlamydia pneumoniae (F) are obligate intracellular bacteria which cause an atypical pneumonia. Less commonly, this infection can cause meningoencephalitis, arthritis, myocarditis and/or Guillain–Barré syndrome.
Respiratory tract infections
A Streptococcus pneumoniae B Moraxella catarrhalis C Haemophilus influenzae D Legionella pneumophila E Mycoplasma pneumonia F Chlamydia pneumoniae G Mycobacterium tuberculosis H Pneumocystis jirovecii I Staphylococcus aureus
2 A 54-year-old woman admitted to the respiratory ward is found to have right sided consolidation on chest X-ray. Histological examination reveals Gram- positive cocci arranged in pairs.
2)A
Streptococcus pneumoniae (pneumococci; A) are alpha-haemolytic Gram-positive cocci arranged in pairs (diploccoci). As Streptococcus pneumoniae are capsulated bacteria, the Quelling reaction in which pneumococci are mixed with anti-serum and methylene blue causes the capsule to swell can be visualized under the microscope. Optochin-sensitivity also differentiates pneumococcus from Streptococcus viridans (also alpha-haemolytic), which is optochin-insensitve. Clinically, lobar consolidation is visible on X-ray, which represents a collection of pus, bacteria and exudate in the alveoli.
Moraxella catarrhalis (B) are aerobic Gram-negative diploccoci. This bacterium is particularly problematic in patients with chronic lung disease and causes exacerbations of chronic obstructive pulmonary disorder (COPD). Other targets of infection include ears, eyes and central nervous system.
Haemophilus influenzae (C) are Gram-negative bacilli that cause influenza (flu) outbreaks annually. Chocolate agar is used as a culture medium. Further oxidase and catalase tests are positive.
Mycoplasma pneumoniae (E) are obligate intracellular bacteria which cause an atypical pneumonia or a mild bronchitis. A cold-agglutinin test can be used for the diagnosis. In rare cases, infection may lead to Stevenson–Johnson syndrome.
Chlamydia pneumoniae (F) are obligate intracellular bacteria which cause an atypical pneumonia. Less commonly, this infection can cause meningoencephalitis, arthritis, myocarditis and/or Guillain–Barré syndrome.
Respiratory tract infections
A Streptococcus pneumoniae B Moraxella catarrhalis C Haemophilus influenzae D Legionella pneumophila E Mycoplasma pneumonia F Chlamydia pneumoniae G Mycobacterium tuberculosis H Pneumocystis jirovecii I Staphylococcus aureus
3 A 65-year-old woman is brought into accident and emergency with severe respiratory distress. The patient’s history revealed that she had been seen by her GP due to a viral infection 2 weeks previously. Histological examination reveals Gram-positive cocci arranged in clusters.
3) I
Staphylococcus aureus (I) are beta-haemolytic Gram-positive cocci arranged in grape-like clusters. All staphylococci are also catalase positive, whereas streptococci are catalase negative. Clinically, S. aureus can cause consolidation, cavitations of the lungs empyema (pus in the pleural space). S. aureus has a number of virulence factors including anti-immune proteins (haemolysins, leukocidins and penicillinase) as well as tissue break-down proteins (hyaluronidase and, staphylokinase and protease).
Moraxella catarrhalis (B) are aerobic Gram-negative diploccoci. This bacterium is particularly problematic in patients with chronic lung disease and causes exacerbations of chronic obstructive pulmonary disorder (COPD). Other targets of infection include ears, eyes and central nervous system.
Haemophilus influenzae (C) are Gram-negative bacilli that cause influenza (flu) outbreaks annually. Chocolate agar is used as a culture medium. Further oxidase and catalase tests are positive.
Mycoplasma pneumoniae (E) are obligate intracellular bacteria which cause an atypical pneumonia or a mild bronchitis. A cold-agglutinin test can be used for the diagnosis. In rare cases, infection may lead to Stevenson–Johnson syndrome.
Chlamydia pneumoniae (F) are obligate intracellular bacteria which cause an atypical pneumonia. Less commonly, this infection can cause meningoencephalitis, arthritis, myocarditis and/or Guillain–Barré syndrome.
Respiratory tract infections
A Streptococcus pneumoniae B Moraxella catarrhalis C Haemophilus influenzae D Legionella pneumophila E Mycoplasma pneumonia F Chlamydia pneumoniae G Mycobacterium tuberculosis H Pneumocystis jirovecii I Staphylococcus aureus
4 A 40-year-old HIV positive man is seen by his GP. The patient admits a 4-week history of cough. The GP requests acid-fast staining of the patient’s sputum.
4) G
Mycobacterium tuberculosis (G) is an acid-fast bacillus which is transmitted via aerosol droplets. Clinical manifestations include fever, cough (with possible haemoptysis), weight loss and night sweats. TB is highly prevalent in HIV patients due to impaired cell-mediated immunity. CXR reveals bihilar lymphadenopathy. Most commonly, Ziehl–Neelson staining is performed on a sputum sample demonstrating acid-fast bacilli, but auramine–rhodamine staining can also be used. Mycobacterium tuberculosis, however, take approximately 6 weeks to culture, and hence faster polymerase chain reaction diagnostic tests are being developed.
Moraxella catarrhalis (B) are aerobic Gram-negative diploccoci. This bacterium is particularly problematic in patients with chronic lung disease and causes exacerbations of chronic obstructive pulmonary disorder (COPD). Other targets of infection include ears, eyes and central nervous system.
Haemophilus influenzae (C) are Gram-negative bacilli that cause influenza (flu) outbreaks annually. Chocolate agar is used as a culture medium. Further oxidase and catalase tests are positive.
Mycoplasma pneumoniae (E) are obligate intracellular bacteria which cause an atypical pneumonia or a mild bronchitis. A cold-agglutinin test can be used for the diagnosis. In rare cases, infection may lead to Stevenson–Johnson syndrome.
Chlamydia pneumoniae (F) are obligate intracellular bacteria which cause an atypical pneumonia. Less commonly, this infection can cause meningoencephalitis, arthritis, myocarditis and/or Guillain–Barré syndrome.
Respiratory tract infections
A Streptococcus pneumoniae B Moraxella catarrhalis C Haemophilus influenzae D Legionella pneumophila E Mycoplasma pneumonia F Chlamydia pneumoniae G Mycobacterium tuberculosis H Pneumocystis jirovecii I Staphylococcus aureus
5 A 36-year-old engineer presents to his GP with a 1-week history of headache, myalgia and cough. Blood tests reveal hyponatraemia. A urinary antigen test is found to be positive.
5) D
Legionella pneumophila (D) is an aerobic Gram-negative rod which causes an atypical pneumonia. It primarily affects those who work with air-conditioning units and can lead to milder Pontiac fever or more severe Legionnaire’s disease. Clinical features of legionellosis are non-specific and may include headache, myalgia, confusion, rhabdomyolysis and abdominal pain. Blood chemistry may reveal hyponatraemia, hypophosphataemia and/or deranged liver enzymes. Diagnosis involves culture of respiratory secretions on buffered charcoal yeast extract agar, although a rapid urinary antigen test can also be used.
Moraxella catarrhalis (B) are aerobic Gram-negative diploccoci. This bacterium is particularly problematic in patients with chronic lung disease and causes exacerbations of chronic obstructive pulmonary disorder (COPD). Other targets of infection include ears, eyes and central nervous system.
Haemophilus influenzae (C) are Gram-negative bacilli that cause influenza (flu) outbreaks annually. Chocolate agar is used as a culture medium. Further oxidase and catalase tests are positive.
Mycoplasma pneumoniae (E) are obligate intracellular bacteria which cause an atypical pneumonia or a mild bronchitis. A cold-agglutinin test can be used for the diagnosis. In rare cases, infection may lead to Stevenson–Johnson syndrome.
Chlamydia pneumoniae (F) are obligate intracellular bacteria which cause an atypical pneumonia. Less commonly, this infection can cause meningoencephalitis, arthritis, myocarditis and/or Guillain–Barré syndrome.
Neonatal and childhood infections
A Rubella B Syphilis C Measles D Hepatitis B E Mumps F Listeria monocytogenes G Cytomegalovirus H Haemophilus influenzae I HIV
1 A 10-year-old boy is brought to see the GP by his mother as he has recently developed parotid swelling associated with a fever. Blood tests reveal a raised amylase level. The boy’s mother reveals that his immunization schedule is not complete as they were living in Tunisia at the time.
1)E
Mumps (E) is spread by droplets in the air which travel via the lungs to parotid tissue and subsequently to distant sites. Clinical features of infection consist of fever, malaise and transient hearing loss. Parotitis is characteristic of mumps infection with unilateral or bilateral swelling and pain on chewing. Plasma amylase levels may be elevated as a result of inflammation of the salivary glands. Complications such as viral meningitis, orchitis/oophoritis, mastitis and arthritis may result from long-standing infection. The MMR vaccine given at 12–18 months has drastically reduced the incidence of mumps.
Hepatitis B (D) may be vertically transmitted from mother to child dur- ing childbirth. Mothers who are HBeAg positive are especially at risk of transmitting the virus; infection may become chronic in 20 per cent of cases.
Syphilis (B) can be congenitally transmitted. Symptoms that may develop in the first few years of life include hepatosplenomegaly, rash, fever and neurosyphilis. Long-term complications include saddle-nose deformity, Higoumenakis’ sign (unilateral enlargement of the clavicle) and Clutton’s joints (symmetrical joint swelling).
Cytomegalovirus (G) may be transmitted in the perinatal period from infected mothers. Presentation may include low birth weight, micro- cephaly, seizures and/or petechial rash.
HIV (I) transmission may occur in utero or during birth. Infected moth- ers are advised to take Zidovudine during pregnancy; the infant is required to take Zidovudine for 6 weeks following birth.
Neonatal and childhood infections
A Rubella B Syphilis C Measles D Hepatitis B E Mumps F Listeria monocytogenes G Cytomegalovirus H Haemophilus influenzae I HIV
2 A 3-week-old baby develops vomiting and is feeding poorly. On examination he has a reduced level of consciousness and an arched back. Analysis of the CSF reveals the presence of Gram-positive rods.
2)F
Listeria monocytogenes (F) is a beta-haemolytic anaerobic Gram-positive rod that can cause meningitis in the neonate to 3 months age group. Listeria monocytogenes may be transmitted vertically from mother to baby in utero (due to the ingestion of infected food by the mother) or during birth (transvaginal transfer). Early signs of meningitis are non-specific in the age group affected (fever, poor feeding, vomiting, seizures and reduced consciousness) whereas late signs include a bulging fontanelle, neck stiffness, opisthotonos (arched back), Brudzinski and Kernig signs positive as well as meningococcaemia.
Hepatitis B (D) may be vertically transmitted from mother to child dur- ing childbirth. Mothers who are HBeAg positive are especially at risk of transmitting the virus; infection may become chronic in 20 per cent of cases.
Syphilis (B) can be congenitally transmitted. Symptoms that may develop in the first few years of life include hepatosplenomegaly, rash, fever and neurosyphilis. Long-term complications include saddle-nose deformity, Higoumenakis’ sign (unilateral enlargement of the clavicle) and Clutton’s joints (symmetrical joint swelling).
Cytomegalovirus (G) may be transmitted in the perinatal period from infected mothers. Presentation may include low birth weight, micro- cephaly, seizures and/or petechial rash.
HIV (I) transmission may occur in utero or during birth. Infected moth- ers are advised to take Zidovudine during pregnancy; the infant is required to take Zidovudine for 6 weeks following birth.
Neonatal and childhood infections
A Rubella B Syphilis C Measles D Hepatitis B E Mumps F Listeria monocytogenes G Cytomegalovirus H Haemophilus influenzae I HIV
3 A 3-year-old girl presents to the GP with a cough, fever and runny nose. On examination, the child has white spots scattered on the buccal mucosa. Her mother admits that she denied her child a certain vaccine due to scares presented by the media.
3)C
Measles (C) is a viral respiratory system infection caused by the genus Morbillivirus. Infection presents with cough, coryza, conjunctivitis and/ or a discrete maculopapular rash. White spots on the buccal mucosa (Koplik spots) are pathognomonic for measles. Complications of measles infection may involve the respiratory (pneumonia and tracheitis) and neurological (febrile convulsions and encephalitis) systems. Subacute sclerosing panencephalitis (SSPE) may occur several years after the primary infection; infection persists in the CNS leading to loss of neurological function, dementia and eventually death.
Hepatitis B (D) may be vertically transmitted from mother to child during childbirth. Mothers who are HBeAg positive are especially at risk of transmitting the virus; infection may become chronic in 20 per cent of cases.
Syphilis (B) can be congenitally transmitted. Symptoms that may develop in the first few years of life include hepatosplenomegaly, rash, fever and neurosyphilis. Long-term complications include saddle-nose deformity, Higoumenakis’ sign (unilateral enlargement of the clavicle) and Clutton’s joints (symmetrical joint swelling).
Cytomegalovirus (G) may be transmitted in the perinatal period from infected mothers. Presentation may include low birth weight, micro- cephaly, seizures and/or petechial rash.
HIV (I) transmission may occur in utero or during birth. Infected mothers are advised to take Zidovudine during pregnancy; the infant is required to take Zidovudine for 6 weeks following birth.
Neonatal and childhood infections
A Rubella B Syphilis C Measles D Hepatitis B E Mumps F Listeria monocytogenes G Cytomegalovirus H Haemophilus influenzae I HIV
4 A 4-year-old boy presents to A&E with a reduced level of consciousness, headache and neck stiffness. Analysis of the CSF reveals the presence of Gram-negative rods. The child’s mother reveals that his immunization record is not complete as they have only migrated from Ethiopia recently.
4) H
Haemophilus influenzae (H) is a Gram-negative rod shaped bacterium that causes meningitis in children older than 3 months who have not been vaccinated. Other organisms that cause meningitis in older children include Streptococcus pneumoniae and Neisseria meningitidis. Diagnosis involves culture of the bacteria using chocolate agar, with subsequent Gram-stain and microscopy. Latex particle agglutination and PCR are more sensitive and specific investigative tests. The Haemophilus influenzae type B (Hib) vaccine has dramatically reduced Hib-related meningitis; the first dose is given when the child is 8 weeks old.
Hepatitis B (D) may be vertically transmitted from mother to child during childbirth. Mothers who are HBeAg positive are especially at risk of transmitting the virus; infection may become chronic in 20 per cent of cases.
Syphilis (B) can be congenitally transmitted. Symptoms that may develop in the first few years of life include hepatosplenomegaly, rash, fever and neurosyphilis. Long-term complications include saddle-nose deformity, Higoumenakis’ sign (unilateral enlargement of the clavicle) and Clutton’s joints (symmetrical joint swelling).
Cytomegalovirus (G) may be transmitted in the perinatal period from infected mothers. Presentation may include low birth weight, micro- cephaly, seizures and/or petechial rash.
HIV (I) transmission may occur in utero or during birth. Infected mothers are advised to take Zidovudine during pregnancy; the infant is required to take Zidovudine for 6 weeks following birth.
Neonatal and childhood infections
A Rubella B Syphilis C Measles D Hepatitis B E Mumps F Listeria monocytogenes G Cytomegalovirus H Haemophilus influenzae I HIV
5 An 8-month old girl is seen by a paediatrician due to concerns about developmental delay. On examination cataracts are noted in both eyes. Echocardiography reveals a patent ductus arteriosus.
5) A
Rubella (German measles; A) is a viral infection which can be congeni- tal or acquired. Congenital rubella syndrome (CRS) occurs in a develop- ing fetus if the mother has contracted rubella in her first trimester. CRS is characterized by sensorineural deafness, eye abnormalities (cataracts, glaucoma, retinopathy) and congenital heart disease (patent ductus arteriosus). Other associations include microcephaly and developmental delay. Acquired rubella is transmitted via the respiratory route. Characteristically, a rash appears on the face which spreads to the trunk and disappears after a few days.
Hepatitis B (D) may be vertically transmitted from mother to child dur- ing childbirth. Mothers who are HBeAg positive are especially at risk of transmitting the virus; infection may become chronic in 20 per cent of cases.
Syphilis (B) can be congenitally transmitted. Symptoms that may develop in the first few years of life include hepatosplenomegaly, rash, fever and neurosyphilis. Long-term complications include saddle-nose deformity, Higoumenakis’ sign (unilateral enlargement of the clavicle) and Clutton’s joints (symmetrical joint swelling).
Cytomegalovirus (G) may be transmitted in the perinatal period from infected mothers. Presentation may include low birth weight, micro- cephaly, seizures and/or petechial rash.
HIV (I) transmission may occur in utero or during birth. Infected moth- ers are advised to take Zidovudine during pregnancy; the infant is required to take Zidovudine for 6 weeks following birth.
Gastrointestinal infections
A Vibrio cholerae B Staphylococcus aureus C Enterobacteriaecae D Listeria monocytogenes E Salmonella enteritidis F Shigellae G Campylobacter jejuni H Giardia lamblia I Entamoeba histolytica
1 A 34-year-old HIV-positive woman is seen in the GP clinic due to 3 days of diarrhoea, headaches and fever. History reveals the patient had recently drunk unpasteurized milk. The causative organism is found to be Beta-haemolytic with tumbling motility.
1) D
Listeria monocytogenes (D) is a -haemolytic anaerobic Gram-positive rod that may cause outbreaks of non-invasive gastroenteritis. Sources include refrigerated food and unpasteurized dairy products. Clinical features of listeria infection include watery diarrhoea, abdominal cramps, headaches and fever, but minimal vomiting. Listeria demonstrates ‘tumbling motility’ as a result of flagellar-driven movements. Neonates and immunocompromised patients are particularly susceptible. Invasive infection can cause more serious problems in these groups including septicaemia, meningitis and encephalitis.
Salmonella typhi (E) infection, also known as enteric fever, multiplies in the Peyer’s patches of the small intestine. Clinical features include slow onset fever, constipation and splenomegaly. Rose spots are pathognomonic.
Shigellae (F) are non-motile, non-hydrogen sulphide producers. The bacteria cause dysentery via invasion of mucosal cells of distal ileum and colon as well as the production of an enterotoxin, known as Shiga toxin.
Campylobacter jejuni (G) are oxidase positive, non-motile bacteria. Transmission occurs via the faecal–oral route, generally due to contamination by dog faecal matter, causing a watery, foul smelling diarrhoea. Complications include Guillain–Barré syndrome and Reiter’s syndrome.
Entamoeba histolytica (I) is a motile trophozite. Ingestion of the cysts leads to colonization of caecum and colon, which may cause a ‘flask-shaped’ ulcer to develop. Clinical features involve dysentery, chronic weight loss and liver abscess formation.
Gastrointestinal infections
A Vibrio cholerae B Staphylococcus aureus C Enterobacteriaecae D Listeria monocytogenes E Salmonella enteritidis F Shigellae G Campylobacter jejuni H Giardia lamblia I Entamoeba histolytica
2 A 10-year-old girl has just returned from a summer swimming camp at Lake Windermere. She presents to accident and emergency with bloody diarrhoea and abdominal pain. Blood tests reveal anaemia and thrombocytopenia.
2) C
Escherichia coli (C) is a Gram-negative rod-shaped bacterium that is a common cause of traveller’s diarrhoea in those returning from abroad. Transmission occurs via food and water that become contaminated with human faeces, as can swimming in contaminated lakes. Enterohaemorrhagic E. coli infection (serotype O157:H7) can lead to haemolytic uraemic syndrome (HUS), characterized by haemolytic anaemia, acute renal failure (uraemia) and a low platelet count (thrombocytopenia). Other diarrhoea-causing strains of E. coli include enterotoxigenic, enteropathogenic and enteroinvasive forms.
Salmonella typhi (E) infection, also known as enteric fever, multiplies in the Peyer’s patches of the small intestine. Clinical features include slow onset fever, constipation and splenomegaly. Rose spots are pathognomonic.
Shigellae (F) are non-motile, non-hydrogen sulphide producers. The bacteria cause dysentery via invasion of mucosal cells of distal ileum and colon as well as the production of an enterotoxin, known as Shiga toxin.
Campylobacter jejuni (G) are oxidase positive, non-motile bacteria. Transmission occurs via the faecal–oral route, generally due to contamination by dog faecal matter, causing a watery, foul smelling diarrhoea. Complications include Guillain–Barré syndrome and Reiter’s syndrome.
Entamoeba histolytica (I) is a motile trophozite. Ingestion of the cysts leads to colonization of caecum and colon, which may cause a ‘flask-shaped’ ulcer to develop. Clinical features involve dysentery, chronic weight loss and liver abscess formation.
Gastrointestinal infections
A Vibrio cholerae B Staphylococcus aureus C Enterobacteriaecae D Listeria monocytogenes E Salmonella enteritidis F Shigellae G Campylobacter jejuni H Giardia lamblia I Entamoeba histolytica
3 An 18-year-old on his gap year in India suddenly develops severe watery diarrhoea. Microscopy of his stool reveals no leukocytes but rods with fast movements.
3) A
Vibrio cholerae (A) are comma-shaped oxidase positive bacteria, causing profuse watery diarrhoea containing no inflammatory cells on microscopy. Transmission occurs via the faecal-oral route. Vibrio cholerae colonizes the small intestinal section of the gut and secretes enterotoxin containing subunits A (active) and B (binding). B subunit binds to GM1 ganglioside on the intestinal epithelial cells. Intracellularly, there is activation of cAMP by A subunit, which causes active secretion of sodium and chloride ions; as a consequence water is lost due to the osmotic pull of NaCl.
Salmonella typhi (E) infection, also known as enteric fever, multiplies in the Peyer’s patches of the small intestine. Clinical features include slow onset fever, constipation and splenomegaly. Rose spots are pathognomonic.
Shigellae (F) are non-motile, non-hydrogen sulphide producers. The bacteria cause dysentery via invasion of mucosal cells of distal ileum and colon as well as the production of an enterotoxin, known as Shiga toxin.
Campylobacter jejuni (G) are oxidase positive, non-motile bacteria. Transmission occurs via the faecal–oral route, generally due to contamination by dog faecal matter, causing a watery, foul smelling diarrhoea. Complications include Guillain–Barré syndrome and Reiter’s syndrome.
Entamoeba histolytica (I) is a motile trophozite. Ingestion of the cysts leads to colonization of caecum and colon, which may cause a ‘flask-shaped’ ulcer to develop. Clinical features involve dysentery, chronic weight loss and liver abscess formation.
Gastrointestinal infections
A Vibrio cholerae B Staphylococcus aureus C Enterobacteriaecae D Listeria monocytogenes E Salmonella enteritidis F Shigellae G Campylobacter jejuni H Giardia lamblia I Entamoeba histolytica
4 A 25-year-old homosexual man presents to his GP with a 3-day history of foul smelling, non-bloody diarrhoea, with abdominal cramps and flatulence. Stool microscopy reveals pear-shaped organisms.
4)H
Giardia lamblia (H) is a pear-shaped trophozite containing two nuclei, four flagellae and a suction disc. Transmission occurs via ingestion of a cyst from faecally contaminated water and food. Trophozites attach to the duodenum but do not invade. Instead, protein absorption is inhibited, drawing water into the lumen of the gastrointestinal tract. G. lamblia must be considered in travellers, hikers and homosexual men. Clinically, foul smelling non-bloody steatorrhoea is produced, with stool containing cysts visible on microscopy.
Salmonella typhi (E) infection, also known as enteric fever, multiplies in the Peyer’s patches of the small intestine. Clinical features include slow onset fever, constipation and splenomegaly. Rose spots are pathognomonic.
Shigellae (F) are non-motile, non-hydrogen sulphide producers. The bacteria cause dysentery via invasion of mucosal cells of distal ileum and colon as well as the production of an enterotoxin, known as Shiga toxin.
Campylobacter jejuni (G) are oxidase positive, non-motile bacteria. Transmission occurs via the faecal–oral route, generally due to contamination by dog faecal matter, causing a watery, foul smelling diarrhoea. Complications include Guillain–Barré syndrome and Reiter’s syndrome.
Entamoeba histolytica (I) is a motile trophozite. Ingestion of the cysts leads to colonization of caecum and colon, which may cause a ‘flask-shaped’ ulcer to develop. Clinical features involve dysentery, chronic weight loss and liver abscess formation.
Gastrointestinal infections
A Vibrio cholerae B Staphylococcus aureus C Enterobacteriaecae D Listeria monocytogenes E Salmonella enteritidis F Shigellae G Campylobacter jejuni H Giardia lamblia I Entamoeba histolytica
5 A 35-year-old woman presents to accident and emergency with fever, diarrhoea and signs of shock. Her husband mentions that she had attended a work colleague’s barbeque the previous day. The consultant believes superantigens are responsible for the patient’s condition.
5)B
Staphylococcus aureus (B) are beta-haemolytic Gram-positive cocci arranged in grape-like clusters. In the gastrointestinal tract, S. aureus produces the exotoxin TSST-1, which acts as a superantigen causing non-specific activation of T cells and subsequent release of IL-1, IL-2 and TNF-alpha. A massive non-specific immune response follows caus- ing shock and multiple organ failure. Enterotoxin produced by bacteria causes vomiting and diarrhoea 12–24 hours after the culprit food has been consumed.
Salmonella typhi (E) infection, also known as enteric fever, multiplies in the Peyer’s patches of the small intestine. Clinical features include slow onset fever, constipation and splenomegaly. Rose spots are pathognomonic.
Shigellae (F) are non-motile, non-hydrogen sulphide producers. The bacteria cause dysentery via invasion of mucosal cells of distal ileum and colon as well as the production of an enterotoxin, known as Shiga toxin.
Campylobacter jejuni (G) are oxidase positive, non-motile bacteria. Transmission occurs via the faecal–oral route, generally due to contamination by dog faecal matter, causing a watery, foul smelling diarrhoea. Complications include Guillain–Barré syndrome and Reiter’s syndrome.
Entamoeba histolytica (I) is a motile trophozite. Ingestion of the cysts leads to colonization of caecum and colon, which may cause a ‘flask-shaped’ ulcer to develop. Clinical features involve dysentery, chronic weight loss and liver abscess formation.
Fungal infections
A Cryptoccus neoformans B Pityriasis versicolour C Aspergillus flavus D Histoplasma capsulatum E Phialophora verrucosa F Tinea capitis G Sporothrix schenckii H Tinea corporis I Candida albicans
1 A 38-year-old man with known HIV presents to his GP with a 1-week history of white coloured creamy deposits inside his mouth. The patient is prescribed an oral nystatin wash.
1) I
Candida albicans (I) can affect both immunocompetent and immunocompromised hosts. In the immunocompetent host, clinical features range from oral thrush (creamy-white patches with red base over mucous membranes of mouth; treated with nystatin) to vaginitis (vaginal inflammation, pruritis and discharge; speculum examination reveals patches of cottage cheese-like clumps fixed to vaginal wall). In immunocompromised patients, C. albicans infection leads to oesophagitis, characterized by odynophagia. Candidaemia can lead to severe flu-like symptoms and can be diagnosed by testing for blood -D-glucan (a component of fungal cell walls).
Histoplasma capsulatum (D) is a fungus transmitted by inhaled spores; it is highly prevalent in the Mississippi River region. Although mostly subclinical, a minority of infections will proceed to a chronic progressive lung disease.
Phialophora verrucosa (E) is a copper coloured soil saprophyte found on rotting wood that causes chromoblastomycosis. Infection is characterized by a warty lesion resembling a cauliflower.
Tinea capitis (F) is a cutaneous dermatophyte fungal infection of the scalp leading to scaly red lesions with loss of hair. It primarily affects children. Infection is characterized by an expanding ring on the scalp.
Tinea corporis (H) is also known as ringworm. It is a cutaneous dermatophyte fungal infection affecting the trunk, arms and legs. It is identified by raised red rings.
Fungal infections
A Cryptoccus neoformans B Pityriasis versicolour C Aspergillus flavus D Histoplasma capsulatum E Phialophora verrucosa F Tinea capitis G Sporothrix schenckii H Tinea corporis I Candida albicans
2 A 45-year-old man with known HIV presents to accident and emergency with headache, nausea, confusion and fever. Investigation of the patient’s CSF with India ink stain reveals yeast cells surrounded by a halo.
2)A
Cryptococcus neoformans (A) is an encapsulated yeast that is transmitted via inhaled spores from pigeon droppings. It is usually asymptomatic in most cases. 75% of cases occur in immunocompromised patients, characterized by the development of sub-acute or chronic meningitis. Cryptococcal meningitis is fatal without treatment due to the associated cerebral oedema and brainstem compression. Diagnosis is made by CSF analysis with India ink stain which reveals yeast cells surrounded by a halo (polysaccharide capsule). A cryptococcal antigen test can also be used which offers higher sensitivity.
Histoplasma capsulatum (D) is a fungus transmitted by inhaled spores; it is highly prevalent in the Mississippi River region. Although mostly subclinical, a minority of infections will proceed to a chronic progressive lung disease.
Phialophora verrucosa (E) is a copper coloured soil saprophyte found on rotting wood that causes chromoblastomycosis. Infection is characterized by a warty lesion resembling a cauliflower.
Tinea capitis (F) is a cutaneous dermatophyte fungal infection of the scalp leading to scaly red lesions with loss of hair. It primarily affects children. Infection is characterized by an expanding ring on the scalp.
Tinea corporis (H) is also known as ringworm. It is a cutaneous dermatophyte fungal infection affecting the trunk, arms and legs. It is identified by raised red rings.
Fungal infections
A Cryptoccus neoformans B Pityriasis versicolour C Aspergillus flavus D Histoplasma capsulatum E Phialophora verrucosa F Tinea capitis G Sporothrix schenckii H Tinea corporis I Candida albicans
3 A 35-year-old woman presents to her GP with hyperpigmented spots on her back. Scrapings of the affected areas reveal a ‘spaghetti with meatballs’ appear- ance under the microscope.
3) B
Pityriasis versicolor (B) is a chronic fungal infection caused by Malassezia furfur, characterized by hypopigmentation (in patients with dark skin tones) and hyperpigmentation (in patients with pale skin tones). Spots affect the back, underarm, arms, legs, chest, neck and rarely the face. Microscopic investigation of the M. furfur with potassium hydroxide reveals a ‘spaghetti with meatballs’ appearance. Wood’s light may also reveal an orange fluorescence in some cases.
Histoplasma capsulatum (D) is a fungus transmitted by inhaled spores; it is highly prevalent in the Mississippi River region. Although mostly subclinical, a minority of infections will proceed to a chronic progressive lung disease.
Phialophora verrucosa (E) is a copper coloured soil saprophyte found on rotting wood that causes chromoblastomycosis. Infection is characterized by a warty lesion resembling a cauliflower.
Tinea capitis (F) is a cutaneous dermatophyte fungal infection of the scalp leading to scaly red lesions with loss of hair. It primarily affects children. Infection is characterized by an expanding ring on the scalp.
Tinea corporis (H) is also known as ringworm. It is a cutaneous dermatophyte fungal infection affecting the trunk, arms and legs. It is identified by raised red rings.
Fungal infections
A Cryptoccus neoformans B Pityriasis versicolour C Aspergillus flavus D Histoplasma capsulatum E Phialophora verrucosa F Tinea capitis G Sporothrix schenckii H Tinea corporis I Candida albicans
4 A 48-year-old HIV positive man who has recently migrated from sub-Saharan Africa presents to accident and emergency with chest pain, shortness of breath, fever and cough. A chest X-ray demonstrates a spherical opacity in the upper left lung field.
4)C
Aspergillus flavus (C) is a fungus that commonly grows on stored grains and can cause a spectrum of disease. Allergic reaction in the airways may cause allergic broncho-pulmonary aspergillosis (ABPA) which occurs due to an IgE mediated type I hypersensitivity reaction leading to bronchospasm and eosinophilia. Infection in pre-formed lung cavities (for example in TB patients) may lead to a fungal ball visible on chest X-ray (aspergilloma). Invasive aspergillosis is a chronic necrotizing infection that may occur in neutropenic patients (chemotherapy) or patients with end stage AIDS (CD4 count <50). Strains may produce the carcinogen aflatoxin, which has a strong association with hepatocellular carcinoma.
Histoplasma capsulatum (D) is a fungus transmitted by inhaled spores; it is highly prevalent in the Mississippi River region. Although mostly subclinical, a minority of infections will proceed to a chronic progressive lung disease.
Phialophora verrucosa (E) is a copper coloured soil saprophyte found on rotting wood that causes chromoblastomycosis. Infection is characterized by a warty lesion resembling a cauliflower.
Tinea capitis (F) is a cutaneous dermatophyte fungal infection of the scalp leading to scaly red lesions with loss of hair. It primarily affects children. Infection is characterized by an expanding ring on the scalp.
Tinea corporis (H) is also known as ringworm. It is a cutaneous dermatophyte fungal infection affecting the trunk, arms and legs. It is identified by raised red rings.
Fungal infections
A Cryptoccus neoformans B Pityriasis versicolour C Aspergillus flavus D Histoplasma capsulatum E Phialophora verrucosa F Tinea capitis G Sporothrix schenckii H Tinea corporis I Candida albicans
5 A 32-year-old gardener presents to his GP with small raised lesions on his left arm. He remembers working in a garden a few days previously which had been swamped with rose-thorns.
5) G
Sporothrix schenckii (Rose garderner’s disease; G) is a fungus found in soil and plants that causes sporotrichosis. A prick by thorns causes nodular lesions to appear on the surface of the skin. Initially the lesions will be small and painless; left untreated they become ulcerated. Infection may also spread to joints, bone and muscle by this route. Inhalation of spores may lead to pulmonary disease and systemic infection may lead to central nervous system involvement. Treatment options include itraconazole, fluconazole and oral potassium iodide.
Histoplasma capsulatum (D) is a fungus transmitted by inhaled spores; it is highly prevalent in the Mississippi River region. Although mostly subclinical, a minority of infections will proceed to a chronic progressive lung disease.
Phialophora verrucosa (E) is a copper coloured soil saprophyte found on rotting wood that causes chromoblastomycosis. Infection is characterized by a warty lesion resembling a cauliflower.
Tinea capitis (F) is a cutaneous dermatophyte fungal infection of the scalp leading to scaly red lesions with loss of hair. It primarily affects children. Infection is characterized by an expanding ring on the scalp.
Tinea corporis (H) is also known as ringworm. It is a cutaneous dermatophyte fungal infection affecting the trunk, arms and legs. It is identified by raised red rings.
CNS infections
A Neisseria meningitides B Herpes simplex virus-2 C Leptospira interrogans D Listeria monocytogenes E Cryptococcus neoformans F Escherichia coli G Streptococcus pneumoniae H Borrelia burgdorferi I Mycobacterium tuberculosi
1 A 45-year-old man presents to his GP with a 2-month history of headache. After a CT scan demonstrates an opacity, a LP is performed and CSF analysis reveals a protein level of 4.5 g/L (0.15–0.4), lymphocyte count 345 (1–5) and glucose 4.0 mmol/L (2.2–3.3).
1) I
Mycobacterium tuberculosis (I) may lead to a subacute or chronic meningitis. Symptoms are non-specific, including fever, headache and confusion. Focal signs may be present as a result of a cerebral granuloma. A tuberculous granuloma that occurs in the cortex of the brain, subsequently rupturing into the subarachnoid space, is termed a Rich focus. Diagnosis of tuberculous meningitis involves a lumbar puncture; the CSF appears colourless and characteristically has high protein, low glucose and raised lymphocyte levels. Nucleic acid amplification tests as well as imaging studies (CT and MRI) can be useful in the diagnostic work-up.
Listeria monocytogenes (D) is a Gram-positive bacillus. Infection usually occurs in neonates, the immunocompromised and elderly. Manifestations include meningitis, encephalitits, pneumonia and septicaemia.
Escherichia coli (F) is a Gram-negative bacillus. The K1 antigen of the bacterium as well as a lack of circulating IgM are responsible for severe meningitis in neonates.
Streptococcus pneumoniae (G) is a Gram-positive alpha-haemolytic diplococcus. It is the most common cause of meningitis in adults together with N. meningitides.
Borrelia burgdorferi (H) is a Gram-negative zoonotic spirochaete that causes Lyme disease. In the late stages of disease the patient will experience arthritis, peripheral neuropathy and/or encephalopathy.
