Microbiology EMQs Flashcards
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
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.
H Pneumocystis jirovecii
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 200 cells/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.
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
A 54-year-old woman admitted to the respiratory ward is found to have right
sided consolidation on chest X-ray. Histological examination reveals Grampositive
cocci arranged in pairs.
A Streptococcus pneumoniae
Streptococcus pneumoniae (pneumococci; A) are α-haemolytic Grampositive
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
α-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.
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
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.
I Staphylococcus aureus
Staphylococcus aureus (I) are β-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 and empyema (pus in the
pleural space). Staphylococcus aureus has a number of virulence factors
including anti-immune proteins (haemolysins, leukocidins and penicillinase)
as well as tissue break-down proteins (hyaluronidase, staphylokinase
and protease).
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
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.
G Mycobacterium tuberculosis
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. Tuberculosis
is highly prevalent in HIV patients due to impaired cell-mediated immunity.
Chest X-ray 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.
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
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.
D Legionella pneumophila
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 nonspecific
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.
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
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 β-haemolytic with
tumbling motility.
D Listeria monocytogenes
Listeria monocytogenes (D) is a β-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.
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
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.
C Enterobacteriaecae
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.
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
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.
A Vibrio cholerae
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.
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
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.
H Giardia lamblia
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.
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
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.
B Staphylococcus aureus
Staphylococcus aureus (B) are β-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-α. A massive non-specific immune response follows causing
shock and multiple organ failure. Enterotoxin produced by bacteria
causes vomiting and diarrhoea 12–24 hours after the culprit food has
been consumed.
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 tuberculosis
A 45-year-old man presents to his GP with a 2-month history of headache.
After a CT scan demonstrates an opacity, a lumbar puncture is performed and
cerebrospinal fluid (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).
I Mycobacterium tuberculosis
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.
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 tuberculosis
A 26-year-old man has recently returned to the UK from a year of working in
Africa where he was taking part in a charity farming project. He presents to
accident and emergency with signs of meningism. A serological microscopic
agglutination test is positive.
C Leptospira interrogans
Leptospira interrogans (C) causes leptospirosis (also known as Weil’s
syndrome). Transmission occurs via contact with animals. Leptospira
are thin aerobic spirochaetes that are tightly coiled. The first stage of
infection is known as the leptospiramic phase, during which the patient
suffers non-specific symptoms such as fever, headache, malaise and
photophobia. In the second immune phase, IgM antibodies have formed
and meningitis, liver damage (causing jaundice) and renal failure may
develop. CSF examination will reveal a raised white cell count. The
microscopic agglutination test is considered the gold standard for diagnosing
leptospirosis.
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 tuberculosis
A 19-year-old woman who has recently started university is brought to accident
and emergency with a headache and a spreading non-blanching rash. Gramstain
of a blood sample reveals the presence of Gram-negative diplococci.
A Neisseria meningitides
Neisseria meningitides (meningococcus; A) is a Gram-negative diplococcus.
Infants aged 6 months to 2 years are most at risk as well as large
numbers of adults living in close quarters. Virulence factors include its
capsule (antiphagocytic), endotoxin (lipopolysaccharide causes haemorrhage
from blood vessels resulting in characteristic petechiae in meningococcaemia)
and IgA1 protease (destroys IgA). Neisseria meningitides
can lead to meningitis (headache, photophobia and neck stiffness)
and meningococcaemia (signs of sepsis with spreading petechial rash).
Neisseria meningitides is grown best on Thayer–Martin VCN media
(only allows Neisseria species to grow).
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 tuberculosis
A 46-year-old man with a history of HIV presents to accident and emergency
with neck stiffness, fever and severe photophobia. Examination of the CSF with
India ink reveals yeast cells surrounded by halos.
E Cryptococcus neoformans
Cryptococcus neoformans (E) is a polysaccharide encapsulated yeast
that causes a subacute or chronic meningoencephalitis. It is transmitted
by inhalation (the source of which is pigeon droppings). Cryptococcus
neoformans is usually asyptomatic, but can be pathogenic in immunocompromised
patients such as those with HIV. As well as meningitis,
C. neoformans can also cause pneumonia, skin ulcers and bone lesions.
Diagnosis is made by examination of CSF; India ink staining reveals
yeast cells with a surrounding halo. Cryptococcal antigen test is, however,
a more sensitive test.
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 tuberculosis
A 35-year-old woman presents to her infectious disease specialist due to recurrent
episodes of meningitis. During her last presentation CSF analysis reveals
a protein level of 0.8 g/L (0.15–0.4), lymphocyte count 290 (0–5) and glucose
2.2 mmol/L (2.2–3.3).
B Herpes simplex virus-2
Herpes simplex virus 2 (HSV-2; B) is the most common cause of viral
meningitis of all the herpes family. HSV-2 is transmitted via sexual
contact or via the mother during birth. The virus infects mucosal epithelial
cells or lymphocytes; retrograde transport occurs from peripheral
nerves to ganglion. Viral causes of meningitis can be diagnosed on
examination of CSF; it appears colourless, with a raised lymphocyte
level, moderately raised protein and normal glucose concentration.
Recurrent aseptic meningitis (Mollaret’s meningitis) can be caused by
both HSV-1 and HSV-2.
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
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.
F Chlamydia trachomatis
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.
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
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.
A Treponema pallidum
Treponema pallidum (A) causes syphilis. Syphilis has three clinical
stages: primary, secondary and tertiary. Primary syphilis is defined by a
firm painless chancre that appears approximately 1 month after sexual
contact and resolves within a few weeks. Secondary syphilis is a bacteri
aemic stage during which a widespread rash forms with lymphadenopathy.
Tertiary 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.
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
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.
H Haemophilus ducreyi
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.
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
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.
C Neiserria gonorrhoeae
Neiserria gonorrhoeae (gonococcus; C) is an intracellular Gramnegative
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 pelvic inflammatory disease in women and epididymitis, prostititis
as well as 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.
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
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.
G Bacterial vaginosis
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 involves
obtaining 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.
