Microbiology SBAs

Question 1

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

Answer 1

C Mycobacterium tuberculosis

This gentleman is most likely suffering from 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). This is often remembered
as ‘buff, rough and tough’. It usually takes approximately 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. There are a few other important
points to remember about staining results for Mycobacterium tuberculosis.
They are classified as acid-fast bacteria, because they are resistant
to losing their colour during staining procedures. The Ziehl–Neelson
stain is the most common method used to stain this type of bacterium,
and they 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 that can be used
for acid-fast bacilli is the auramine stain, which also binds to mycolic
acids to give a yellow fluorescence.

Question 2

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 5.8 mm. 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

Answer 2

B He has been exposed to TB

The Mantoux test is a diagnostic test for tuberculosis. It consists of
an intradermal injection of 0.1 mL 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 chest radiograph consistent
with prior TB
• Patients with organ transplants
• People who are immunosuppressed for other reasons (for example
taking the equivalent of >15 mg/day of prednisone for 1
month or longer)

2 An induration of 10 mm or more is considered positive in:
• Recent immigrants (

Question 3

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

Answer 3

D Streptococcus pneumoniae

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).

Question 4

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.

Achest 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

Answer 4

A Klebsiella pneumoniae

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 production
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.

Question 5

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

Answer 5

C Staphylococcus aureus

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.

Question 6

A patient with shingles is treated with an anti-viral. The drug used is a guanosine
analogue and acts as a substrate for viral thymidine kinase. The most likely
drug she has been given is:

A Foscarnet

B Lamivudine

C Cidofovir

D Acyclovir

E Ganciclovir

Answer 6

D Acyclovir

Acyclovir (D) is a guanosine analogue that causes obligate chain termination
when it attaches to DNA. It is phosphorylated by the enzyme
thymidine kinase found in viruses, which is far more effective than
the cellular thymidine kinase for this process. This means that normal
cells which are not infected by the virus are not affected as much by acyclovir, as there is no viral thymidine kinase present. The acyclovir
monophosphate which then forms is further phosphorylated to a diphosphate
and then to a triphosphate by the cellular thymidine kinase. This
triphosphate potently inhibits viral DNA polymerase, leading to chain
termination. It is effective against the herpes viruses, for example herpes
simplex and herpes zoster which causes shingles.

Question 7

According to the UK immunization schedule, which vaccine should be given to a
2-month-old baby who has already received DTaP (diptheria, tetanus, pertussis),
IPV (polio) and Hib (haemophilus influenzae type B) vaccines?

A Pneumococcus

B MMR

C Meningitis C

D BCG

E Hepatitis B

Answer 7

A Pneumococcus

The current UK immunization schedule is as follows:
• Two months: Hib/IPV/DTaP/PCV
• Three months: Hib/IPV/DTaP/Men C
• Four months: Hib/IPV/DTaP/PCV/Men C
• Twelve months: Hib/Men C
• Thirteen months: MMR/PCV
• Three years four months old or soon after: MMR/DTaP/IPV
• 13–18 years: Booster Diptheria and tetanus/IPV

Question 8

A 24-year-old sexually active woman presents to her GP with dysuria. A urinary
tract infection is diagnosed. Which of the following is the most likely causative
agent?

A Enterobacter

B Escherichia coli

C Klebsiella pneumoniae

D Staphylococcus saphrophyticus

E Proteus mirabilis

Answer 8

B Escherichia coli

The most common cause of a urinary tract infection in all groups of
patients is Escherichia coli (B). Do not be misled by the fact that the
patient is a young, sexually active woman. The E. coli bacterium is a
lactose-fermenting Gram-negative rod. It has various properties that
aid its pathogenesis: a flagellum to enable it to move upstream, fimbrae
so that it can adhere to the urothelium, and haemolysin to form
pores in white blood cells. It also has a protective capsule called the
K-antigen. The other lactose fermenting organisms are Klebsiella and
Enterobacter, whilst non-lactose fermenting organisms include Proteus
and Pseudomonas. Lactose fermenting organisms turn MacConkey agar
pink, whereas non-lactose fermenters do not. Useful investigations for
urinary tract infections can include a urine dipstick to look for nitrites
and leukocytes, and urine cultures looking for a bactiuria of greater
than 105 colony forming units

Question 9

A 44-year-old woman patient returns from her holiday in India with a 2-day
history of watery, offensive diarrhoea, bloating, excessive flatulence and abdominal
pain. The GP obtains a stool sample. Microscopy reveals a flagellate pearshaped
protozoan. The most likely organism implicated is:

A Bacillus cereus

B Salmonella enteritidis

C Giardia lamblia

D Entamoeba histolytica

E Cryptosporidium parvum

Answer 9

C Giardia lamblia

Giardia lamblia (C) is a flagellated protozoan parasite which causes
giardiasis. It attaches to the small bowel wall, but does not invade it.
If you can remember this fact, you will find it easier to remember that
it interferes with absorption, and so leads to the classic symptoms of
weight loss, flatulence, chronic diarrhoea and bloating, as in the patient
in this question. Because it does not invade the small bowel wall, the
diarrhoea is not bloody but it is watery. Microscopy of a stool sample
may show a pear-shaped protozoan. If you imagine a pear making you
feel very bloated, you will remember this fact which often crops up in questions! Very rarely, a string test may be done if other methods to
detect the parasites fail but there is still a high index of clinical suspicion.
A gelatine capsule attached to a long string is swallowed, with the
end of the string remaining outside the mouth and taped to the patient’s
cheek. It remains in place for about 4–6 hours, before the end is examined
under the microscope. Treatment of giardiasis is typically oral
metronidazole.

Question 10

A 21-year-old medical student returns from her elective in India with a history
of abdominal cramps, vomiting, fevers and profuse, watery stools which she
describes as resembling ‘rice-water’. The GP obtains a stool sample. Analysis
reveals curved, comma shaped organisms that were shown to be oxidase positive.
The most likely organism implicated is:

A Hepatitis A

B Clostridium difficile

C Yersinia enterocolitica

D Campylobacter jejuni

E Vibrio cholerae

Answer 10

E Vibrio cholerae

Vibrio cholerae (E) causes profuse watery diarrhoea and vomiting. It can
in fact be one of the most rapidly fatal infectious illnesses if not treated,
because of the severe dehydration causing circulatory shock. The bacteria
produce a toxin which has an A and a B subunit. It is the A subunit
which activates a G protein and results in the production of cAMP,
which initiates the secretion of Na+, K+, Cl-, and HCO3
- into the small
intestine lumen. Most people only have a mild illness which simply resembles other diarrhoeal illnesses. Sometimes, as in this case, the diarrhoea
is profuse and is known colloquially as ‘rice-water’ stools because
of its appearance. The diagnosis is predominantly clinical, but if stool
culture is performed the classical appearance will be of curved shaped,
oxidase-positive organisms. You can remember this as the Cholera
Comma! Rehydration therapy forms the mainstay of treatment.

Question 11

A 35-year-old HIV-positive man presents to his GP complaining of a general
feeling of tiredness, weight loss and night sweats. On examination there is hepatosplenomegaly
and hyperpigmentation of the skin. The most likely diagnosis is:

A Visceral leishmaniasis

B Cutaneous leishmaniasis

C Mucocutaneous leishmaniasis

D Malaria

E Schistosomiasis

Answer 11

A Visceral leishmaniasis

Leishmaniasis is transmitted by phlebotomine sandflies and occurs in
Africa, America and the Middle East. Visceral leishmaniasis (A) is also
known as ‘Kala-azar’, and the most common clinical features include
fever and splenomegaly. Hepatomegaly, skin hyperpigmentation and dry
warty skin occur less frequently, and bone marrow invasion can result in pancytopenia. It can be mistaken for malaria, which is dangerous as
it can be fatal if left untreated. L. donovani and L. infantum are thought
to cause the disease in Africa, Asia and Europe, whilst L. chagasi is
implicated in South America.

Question 12

A 22-year-old student presents to accident and emergency with a raised, erythematous,
scaly ulcer on his forearm which has not been healing. On examination
he is also found to have lymphadenopathy. He gives a history of recently returning
from a 2-month trek in the rainforests of South America. Tissue is aspirated
from the margin of the ulcer, and the organism is cultured in Novy–MacNeal–
Nicolle medium. The organism implicated is:

A Toxoplasma gondii

B Treponema pallidum

C Leishmania dovani

D Leishmania major

E Leishmania braziliensis

Answer 12

D Leishmania major

The picture described is consistent with cutaneous leishmaniasis, the
most common form of leishmaniasis. An itchy, scaly papule develops
at the bite site and develops into a crusty ulcer with raised edges. Local
lymphadenopathy can also occur, but the lesion usually heals within
8 months leaving a depigmented scar called an oriental sore. The organisms
implicated are Leishmania major (D) and L. tropica. You can
remember this if you picture lots of skin lesions cropping up in travellers
from the ‘major tropics’! It is found in many countries, ranging
from South America to the Middle East. Diagnosis can be by Giemsa
staining of slit skin smears, or from tissue aspirated from the ulcer.
The organism can be cultured on Novy–Macneal–Nicolle medium as
described in the question.

Question 13

A 35 year-old male clothing merchant has returned to the UK 2 weeks ago
from a visit home to Syria. A week later he presents with flu-like symptoms,
drenching
sweats and a recurring fever and is beginning to complain of lower
back pain. After further questioning, he mentioned that he worked on a farm
during his trip. He is successfully treated with oral doxycycline and gentamicin.
What is the most likely diagnosis?

A Malaria

B Tuberculosis

C Influenza

D Brucellosis

E Typhoid

Answer 13

D Brucellosis

The Brucella species are Gram-negative, rod shaped, intracellular bacteria
that cause a highly contagious zoonosis known as brucellosis (D).
The causative agent in cattle is B. abortis, but in dogs it is B. canis.
Infection in cattle can lead to miscarriages, hence the name ‘abortis’.
Infection is usually contracted from unsterilized milk, cheese or meat.

Clinical features of brucellosis can include a long history of undulating
fevers, arthralgia and myalgia, weight loss, fatigue, lymphadenopathy,
sacroilitis and depression. Many cases present as pyrexia of unknown
origin. Hepatomegaly and/or splenomegaly can sometimes be found on
examination.

Question 14

A 50-year-old man has returned from hiking a segment of the Appalachian Trail
on the Eastern coast of the USA during the summer months. Ten days later he
presents to casualty with flu-like illness and a rash showing some central fading.
What is the most likely organism implicated?

A Herpes simplex

B Epstein–Barr virus

C Streptococcus pyogenes

D Treponema pallidum

E Borrelia burgdorferi

Answer 14

E Borrelia burgdorferi

Borrelia burgdorferi (E) is a Gram-negative bacterium that causes Lyme
disease. It is a spirochaete, which is the name for a group of bacteria
that are helically coiled in shape. Lyme disease is actually thought to
be the most common vector borne disease in England and Wales. It is
named after a town called Lyme in Connecticut, where the disease was
first seen. The vector is a tick called the Ixodes tick, which can be found
on deer and rodents.

Lyme disease is a multisystemic disorder which has three main stages: the
local stage, disseminated stage and a late stage. The local stage involves
a characteristic skin lesion called erythema chronicum migrans, usually
appearing 7–10 days after the initial infection. It usually starts off as a
red macule or papule, and approximately 1 week later expands to leave
a target appearance with an area of central fading. Other symptoms at
this stage are usually constitutional, such as a fever and headache. The
somewhat unusual features of the next stage can be remembered using
the word PEACH: Peripheral neuropathy, Erythema chronicum migrans
(persists in this stage), Arthritis, Cranial nerve palsies and Heart block.
Finally, the late stage can include persistent arthritis and chronic encephalitis.
Treatment is with oral antibiotics, usually doxycycline.

Question 15

A 26-year-old squash player is admitted with a red, swollen left knee. He reports
no history of trauma. On examination he has a temperature of 38°C. A joint
aspirate is taken. What is the most likely causative organism?

A Neisseria gonorrhoeae

B Staphyloccocus aureus

C Haemophilus influenzae

D Streptococcus viridans

E Chlamydia trachomatis

Answer 15

A Neisseria gonorrhoeae

The most common cause of septic arthritis in young, sexually active
adults is Neisseria gonorrhoeae (A). A Gram-stain of this aspirate would
reveal Gram-negative diplococci. It is less likely for this organism to
lead to joint destruction than a staphylococcal arthritis. The two forms
of disseminated gonoccocal infection are the septic arthritis form (as
described in this case), and the bacteraemic form. Other clinical features
of the bacteraemic form might include a migratory polyarthralgia and a
vesicular or papular rash.

Question 16

A 26-year-old squash player is admitted with a red, swollen left knee. He reports
no history of trauma. On examination he has a temperature of 38°C. A joint
aspirate is taken which grows Gram-negative diplococci. What is the antibiotic
treatment regimen of choice for this patient?

A Oral flucloxacillin for 4–6 weeks

B IV flucloxacillin for 4–6 weeks

C IV flucloxacillin for 2–4 weeks

D IV flucloxacillin and vancomycin for 6–8 weeks

E IV cefotaxime for 4–6 weeks

Answer 16

E IV cefotaxime for 4–6 weeks

The patient in this question is presenting with septic arthritis, and the
most likely cause given the joint aspiration findings of Gram-negative
diplococci is Neisseria gonorrhoeae. The British National Formulary
(BNF) advises the use of intravenous cefotaxime for 4–6 weeks (E) if
gonococcal arthritis or a Gram-negative infection is suspected. The BNF
is a good source of information for looking up the latest guidelines
regarding antibiotic treatment regimens for common types of infection.
Cefotaxime is a third generation cephalosporin. Cephalosporins are part
of the beta-lactam group of antibiotics which work by inhibiting cell
wall synthesis. The penicillins are also part of this group. There are different
generations of cephalosporins, with those of later generations
having increasing Gram-negative but decreasing Gram-positive cover.
Cefotaxime is also used to treat meningitis and gonorrhoea. Some of the
other commonly used third generation cephalosporins are ceftizoxime
and ceftriaxone – you can remember these because they all have a ‘t’ in
their names, just like in ‘third’ generation.

Question 17

You order hepatitis B serology tests for one of your patients, a 24-year-old man
who is an intravenous drug user. The results that come back from the laboratory
are as follows:

• HBsAg = positive
• Anti-HBs = negative
• HBeAg = positive
• Anti-HBe = negative
• Anti-HBc IgM = negative
• Anti-HBc IgG = positive

What is the most likely diagnosis based on these results?

A The patient has chronic hepatitis B infection which is currently highly
infectious

B The patient has chronic hepatitis B infection which is not currently
infectious

C The patient has acute hepatitis B infection which is not currently infectious

D The patient is immune due to hepatitis B vaccination

E The patient is immune due to natural infection

Answer 17

A The patient has chronic hepatitis B infection which is currently highly
infectious

The HBsAg positive indicate that the patient has hepatitis B, and the
HBeAg indicates that it is highly infectious (A). The anti-HBc IgG is also
a marker that it is a chronic infection.
The different hepatitis B surface antigens and antibodies can become
quite confusing, but are often asked about in exam questions. Here is a
summary of what you should know:
• HBsAg – The ‘s’ stands for surface, and refers to a protein on the
surface of the virus. It is the first detectable antigen to appear after
someone has been infected, and can be positive in acute or chronic
disease. Patients who still carry this antigen after 6 months are
termed hepatitis carriers. It is this antigen that is used to make the
hepatitis B vaccine
• Anti-HBs – This is an IgG antibody that appears after the host has
cleared the infection, and indicates recovery. It is also found in a
person who has been vaccinated against hepatitis B (D)
• HBeAg – the ‘e’ antigen is often used as a marker of infectivity, as
it is only found in the blood when the virus is actively replicating.
If you find this hard to remember, think of the ‘e’ standing for ‘eek!
I’m infectious!’ If the patient was not infectious (B), this would not
be present
• Anti-HBc IgM – this indicates that the patient has recently been
infected with hepatitis B, and is a marker of acute infection (C)
• Anti-HBc IgG – this is produced in response to the core antigen,
and often persists for life. You can remember this as the ‘c’ standing
for ‘chronicity’, as it is the difference between IgM and IgG antibodies
which can tell you whether the infection is acute or chronic. And
to remember which way round it is, think of ‘My Gosh, he’s chronic!’
If the patient was immune from natural infection (E), HBsAg
would not be positive, but anti-HBc IgG would be.

Question 18

You order hepatitis B serology tests for one of your patients, a 24-year-old man
who is an intravenous drug user. The results that come back from the laboratory
are as follows:

• HBsAg = negative
• Anti-HBs = positive
• HBeAg = negative
• Anti-HBe = negative
• Anti-HBc IgM = negative
• Anti- HBc IgG = negative

What is the most likely diagnosis based on these results?

A The patient has chronic hepatitis B infection which is currently highly
infectious

B The anti-HBs is a false positive result

C The patient has a resolved hepatitis B infection

D The patient is immune due to hepatitis B vaccination

E The patient is immune due to natural infection

Answer 18

D The patient is immune due to hepatitis B vaccination

Remember from the previous question that the anti-HBs antibody
appears after the host has cleared the infection, and indicates recovery.

It is also found in a person who has been vaccinated against hepatitis B
(D). If you get an exam question which only has the anti-HBs positive,
think of vaccination! Levels of this antibody are measured to see if the
patient has responded adequately to the vaccine.

Question 19

A 79-year old woman is admitted to the hospital for treatment of pneumonia
and is commenced on intravenous antibiotic therapy. Her respiratory symptoms
begin to improve, but 5 days later she develops profuse diarrhoea. The most
appropriate treatment is:

A Oral metronidazole for 7 days

B Oral metronidazole for 14 days

C Isolation and treatment with intravenous fluids

D IV metronidazole for 7 days

E Oral co-amoxiclav for 7 days

Answer 19

B Oral metronidazole for 14 days

Broad spectrum antibiotics, such as those used for pneumonia, can
eradicate a patient’s normal gut flora and therefore increase their susceptibility
to Clostridium difficile infection. This is particularly true of
penicillin derivatives (as was most likely used to treat her pneumonia),
clindamycin, and third generation cephalosporins. It classically presents
with profuse watery diarrhoea, usually of acute onset. The most common
time for it to occur is 4–9 days after the antibiotics are started, but
it can occur up to 2 months after discontinuing treatment. Clostridium
difficile is a Gram-positive, anaerobic rod-shaped bacterium. The gold
standard for diagnosis is detection of the C. difficile toxin in a stool
sample.

Question 20

A 79-year old woman is admitted to hospital for treatment of pneumonia and is
commenced on intravenous antibiotic therapy. Her respiratory symptoms begin
to improve, but 5 days later she develops profuse diarrhoea. After treatment with
oral metronidazole she shows gradual improvement, but the profuse diarrhoea
returns 2 weeks later. The same organism is found to be responsible. The most
appropriate course of action is:

A Oral metronidazole for 7 days

B Oral metronidazole for 14 days

C Isolation and treatment with intravenous fluids

D IV metronidazole for 7 days

E Oral vancomycin for 14 days

Answer 20

B Oral metronidazole for 14 days

This patient’s repeated diarrhoea may be caused by persistent infection
with Clostridium difficile (spore germination), new infection or resistant
bacteria. Current guidelines recommend the use of a repeat course of
metronidazole for the treatment of recurrent C. difficile infection (B).
As explained previously, a 7-day course of metronidazole (A) is not
considered a sufficient duration of treatment to eradicate the bacterium.
Again, isolation and IV fluid resuscitation (C) is necessary but
not adequate as a single measure in the management of this woman.
Intravenous metronidazole (D) is only needed if a patient is not
responding to vancomycin, the infection is life-threatening, or for
patients with ileus.
Oral vancomycin for 10–14 days (E) is given for:
• Third or subsequent episodes
• Severe infection
• Infection not responding to metronidazole
• patients who cannot tolerate metronidazole

Question 21

A 65-year old retired mechanic is brought by his family to his GP due to their
concern over his recent increase in confusion. This has occurred rapidly over the
past 4 months, and he now struggles to recognize members of his family. His
daughter also reports occasionally seeing intermittent, jerky movements of both
his arms. The GP organizes a CT scan and dementia screen, which are both found
to be normal. Which is the next most useful diagnostic test for the GP to order?

A MRI brain

B Electroencephalogram

C Electrocardiogram

D Ultrasound scan of both carotids

E Tonsillar biopsy

Answer 21

B Electroencephalogram

The key here is the rapidly progressive nature of the condition in a relatively
young patient. He shows the characteristic sudden decline in cognitive
function, combined with the presence of myoclonic jerks and the lack of positive investigation results so far. This is highly suggestive of
sporadic Creutzfeldt–Jakob disease (CJD), the name given to a common
group of prion diseases. The word prion is derived from the words ‘protein’
and ‘infection’, and it so follows that a prion is a highly infectious
agent composed of protein.
There are essentially three different forms of CJD which you should be
aware of:

1 Sporadic Creutzfeldt–Jakob Disease (80 per cent)
2 Acquired (

Question 22

A 61-year-old patient has recently been diagnosed with sporadic CJD. His GP is
keen to do a lumbar puncture. Which of the following statements is true regarding
this investigation in this situation?

A The lumbar puncture is used to look for the levels of protein, glucose and
polymorphs

B The lumbar puncture is used to look for the levels of a
protein called 14-3-3

C A lumbar puncture is the most specific test for variant CJD

D The lumbar puncture is not useful in sporadic CJD, but is an important test
in variant CJD

E A tonsillar biopsy would be a more useful test than a lumbar puncture for
sporadic CJD

Answer 22

B The lumbar puncture is used to look for the levels of a protein called 14-3-3

The lumbar puncture in CJD is used to analyze the CSF for a protein
named ‘14-3-3’ (B). Note that routine analysis of the cerebrospinal fluid
(CSF) is normal in CJD, therefore looking at levels of protein, glucose
and polymorphs (A) would not be useful to distinguish between possible
causative agents of the clinical features as it is in meningitis.

Question 23

A 16-year-old student complains of a headache of recent onset at school. He
is taken to accident and emergency and on examination has a temperature of
37.6°C. A lumbar puncture is performed, and the results are as follows:

• Appearance: Clear fluid
• Protein: 0.82 g/L
• WCC: 90.5 × 107 (>95 per cent lymphocytes)

What is the most likely diagnosis?

A Subarachnoid haemorrhage

B Tension headache

C Bacterial meningitis

D Viral meningitis

E Tuberculous meningitis

Answer 23

E Tuberculous meningitis

In this context, the two most immediately worrying diagnoses for the
onset of an acute headache are a subarachnoid haemorrhage and bacterial
meningitis as both of these may be fatal if rapid intervention does
not occur.

Cause Appearance Neutrophil count (x 106/L)
Lymphocyte count (x 106/L) Protein (g/L) Glucose (mmol/L)
Normal Clear 0

Question 24

A 42-year-old alcoholic is admitted with abdominal distension. The shifting
dullness test is positive and he is found to have diffuse abdominal tenderness.
His observations are as follows: pulse 115, blood pressure 116/83, temperature
37.9°C. The next best course of action is:

A Begin therapeutic paracentesis

B Observe, administer analgesia and closely monitor his
vital signs

C Commence intravenous spironolactone

D Commence intravenous amoxicillin

E Commence intravenous cefotaxime

Answer 24

E Commence intravenous cefotaxime

This patient is presenting with features suggestive of spontaneous bacterial
peritonitis (SBP), which is a form of peritonitis in the absence of a
contiguous source of infection. This usually results from the development
of portal hypertension in patients with chronic liver disease. This
group of patients are particularly susceptible as they are often immunocompromised.
The pyrexia and tachycardia, in conjunction with the clinical features of
abdominal tenderness and ascites, make this the most likely diagnosis in
this patient. Other typical clinical features might include nausea, vomiting,
confusion, general malaise or features of hepatic encephalopathy.
In approximately 15 per cent of patients SPB can be asymptomatic.

The most common organisms isolated in patients with SBP include
E. coli, Gram-positive cocci and enterococci. Although local antibiotic
guidelines may differ, of the options listed cefotaxime (E) is one of the
most extensively studied and has been proven to be effective.

Question 25

A 63-year-old asymptomatic housewife is referred to a gastroenterologist after
her GP found that she had abnormal liver function tests on a routine blood test.
A thorough history reveals that she received a blood transfusion during her pregnancy
in 1979. Further tests confirm that she has contracted hepatitis C. She is
commenced on a course of anti-viral treatment. Which of the following factors is
most significant in influencing her chance of clearing the virus?

A The length of time between contracting the disease and being diagnosed

B The route by which she contracted the disease

C Her liver function test results

D The virus genotype

E The level of alpha-feto-protein

Answer 25

D The virus genotype

Hepatitis C is a single stranded RNA virus that is similar in structure
to the ‘flaviviruses’. It can cause a slowly progressive disease of the
liver that is frequently asymptomatic and which cannot be vaccinated
against. Routes of transmission include:
• blood products (before 1991, when screening of blood donors for the
disease was introduced)
• intravenous drug use
• sexual transmission
• vertical transmission
• less commonly: needle-stick injuries, tattoos

Question 26

A 63-year-old asymptomatic housewife is referred to a gastroenterologist after her
GP found that she had abnormal liver function tests on a routine blood test. A thorough
history reveals that she received a blood transfusion during her pregnancy in
1979. The best test to confirm whether the patient has hepatitis C would be:

A Liver biopsy

B Anti-hepatitis C antibodies

C Alanine aminotransferase levels

D Hepatitis C RNA PCR

E Viral genotyping

Answer 26

D Hepatitis C RNA PCR

Hepatitis C RNA PCR (D) – This can be used to differentiate between a
current and past infection. A quantitative test to detect the number of
hepatitis C RNA particles (called the ‘viral load’) can also be performed.
This can be very useful to detect a patient’s response to the anti-viral
treatment. Therefore, this is the best diagnostic test for hepatitis C

Question 27

A 33-year-old backpacker visits his GP complaining of feeling weak, lethargic
and feverish since he returned from his trip to South Africa 3 months previously.
He is accompanied by his wife, who reports a change in his behaviour and disturbed
sleeping pattern since his return. On examination, his GP discovers that he
has enlarged cervical lymph nodes, and there is a small chancre on his forearm
that is approximately 2 cm in diameter. The most likely causative organism is:

A Plasmodium falciparum

B Trypanosoma brucei gambiense

C Trypanosoma brucei rhodesiense

D Trypanosoma cruzi

E Leishmania infantum

Answer 27

C Trypanosoma brucei rhodesiense

Human African trypanosomiasis is also known as sleeping sickness, and
is an infection transmitted by the tsetse fly in sub-Saharan Africa. There
are two main types:

Trypanosoma brucei rhodesiense (C) is found in south and eastern
Africa, accounts for under 5 per cent of cases, and causes an acute
infection with symptoms appearing over a few weeks or months.
You can remember this as rhodesiense causes a rapid infection. As
this patient’s symptoms appeared 3 months after returning from his
travels, this is more likely to be the causative agent here

1 Trypanosoma brucei gambiense (B) is found in west and central Africa,
is responsible for over 95 per cent of cases, and causes a chronic
infection. It can take months or even years for symptoms to appear.
You can remember this as gambiense causes a gradual infection

Question 28

A 20-year-old student seeks medical attention due to recent difficulty in swallowing,
and severe weight loss. A thorough travel history reveals that he
returned several months ago from a gap year in Brazil. During his trip he
remembers becoming unwell at one point with a fever, diarrhoea, vomiting and
swollen eyelids, but this resolved in approximately 3 weeks with no treatment. A
chest x-ray is ordered as one of his investigations, and this reveals marked dilatation
of his oesophagus. The vector responsible for transmitting this disease is:

A Tsetse fly

B Reduviid bug

C Sandfly

D Aedes mosquito

E Ixodes tick

Answer 28

B Reduviid bug

Trypanosoma cruzi is responsible for causing Chagas disease, a potentially
life-threatening disease which is spread by reduviid bugs (B) in Brazil. These are also known as ‘kissing bugs’. A red nodule, called a
chagoma, can appear at the site of the bite.
There are two forms of the disease: acute and chronic. In the acute phase,
patients may experience non-specific symptoms such as fever, lethargy,
diarrhoea, and vomiting. A characteristic feature, but one which occurs
in less than 50 per cent of cases, is a purplish swelling of the eyelids
(called Romana’s sign). To put this all together, picture Tom Cruise
(Trypanosoma cruzi) starring in a gladiator film as a Roman (Romana’s sign) wearing purple sunglasses (swollen eyelids) and being kissed
(kissing bugs) by lots of fans ‘ready with their video cameras’ (reduviid!)

Question 29

A 46-year-old Somalian woman presents to her GP with a dry cough and weight
loss of 5 kg over 3 weeks. She is sent to the hospital, and a chest x-ray reveals
cavitating lung lesions. The most appropriate therapy is:

A Rifampicin and isoniazid for 6 months, ethambutol and pyrazinamide for
2 months

B Rifampicin and isoniazid for 2 months, ethambutol and pyrazinamide for
6 months

C Rifampicin and pyrazinamide for 4 months, ethambutol and isoniazid and
for 2 months

D Rifampicin and streptomycin for 4 months, pyrazinamide and ethambutol
for 2 months

E Rifampicin, isoniazid, ethambutol and pyrazinamide for 6 months

Answer 29

A Rifampicin and isoniazid for 6 months, ethambutol and pyrazinamide for
2 months

Current guidelines in the UK recommend the following antibiotic treatment
for pulmonary tuberculosis:
• Isoniazid and rifampicin for 6 months
• Pyrazinamide and ethambutol for the first 2 months

Question 30

A 46-year-old Somalian woman presents to her GP with a dry cough and weight
loss of 5 kg over 3 weeks. She is sent to the hospital, and a chest x-ray reveals
cavitating lung lesions. She is started on a course of anti-tuberculous medication.
Which of the following statements about this regimen is true?

A Liver function tests only need to be checked in those with pre-existing liver
disease

B Ethambutol can cause a peripheral neuropathy

C Pyridoxine should always be given with isoniazid
treatment

D Rifampicin can cause optic neuritis

E Ethambutol should be avoided in renal failure

Answer 30

E Ethambutol should be avoided in renal failure

Remember that treatment for pulmonary TB usually consists of two
phases – an initial phase with rifampicin, isoniazid, pyrazinamide and
ethambutol for 2 months, and then a continuation phase with rifampicin
and isoniazid only for 4 months.
Streptomycin and ethambutol are two anti-tuberculous drugs which
should preferably be avoided in patients with renal impairment (
E).
If they have to be used the dosage should be reduced and the plasma
drug concentration closely monitored. A patient’s renal function
should be checked routinely before anti-tuberculous medication is
started.
The side effect that is particularly worrying with the use of ethambutol
is its ocular toxicity, and this is more likely in renal impairment as it is
renally excreted. This can present with changes in visual acuity, colour
blindness and restriction of visual fields. Therefore a patient’s visual
acuity should be assessed with a Snellen chart prior to starting treatment,
and they should be strongly advised to stop the medication and
seek advice if they become aware of any change in their vision

Question 31

A 35-year-old banker develops a fever, vomiting and diarrhoea after a barbeque.
This resolves within 2 weeks, but he then suddenly develops unilateral facial
weakness. This is followed by severe muscle weakness which rapidly spreads over
the next 5 days from his feet and legs to his trunk. The most likely diagnosis is:

A Polio

B Lyme disease

C Guillan–Barré syndrome

D Haemolytic uraemic syndrome

E Influenza

Answer 31

C Guillan–Barré syndrome

This scenario is characteristic of Guillan–Barrè syndrome. If you remember
that this disease is also known as AIDP – acute inflammatory demyelinating
polyradiculopathy – you can remember the underlying pathology
more easily. It is usually triggered by an infection, and it is thought
that a suppressed T-cell response results in an immunological reaction
that targets the peripheral nerves.
The triggering infection is most commonly Campylobacter jejuni (as
alluded to here), but other common causes can include Mycoplasma
pneumoniae and viruses such as cytomegalovirus and influenza

Question 32

A young girl returns from visiting her relatives in India, feeling feverish and
with flu-like symptoms. A diagnosis of malaria is suspected. Her fevers started on
Monday, regressed for a few days and then returned on Thursday. She was well
again over the weekend, and was then brought to the GP the following Monday
when her fever had again returned. The most likely causative agent in this case is:

A Plasmodium falciparum

B Plasmodium vivax

C Plasmodium ovale

D Plasmodium malariae

E Plasmodium knowlesi

Answer 32

D Plasmodium malariae

Plasmodium
falciparum (A)
7–14 days Malignant
tertian
This is the most severe form

Plasmodium
vivax (B)
12–17 days Benign
tertian
Relapse can occur with these forms because
the parasite can lie dormant in the liver, and
can produce symptoms months or years later

Plasmodium
ovale (C)
15–18 days Benign
tertian

Plasmodium
malariae (D)
18–40 days Benign
quartan
Relapse can occur with this too, but this time
the parasites lie dormant in the blood

Plasmodium
knowlesi (E)
12 days Quotidian
(daily)
This form mainly occurs in southeast Asia
(such as in Borneo), and not in Africa. It does
not normally relapse

Question 33

A young girl returns from visiting her relatives in India, feeling feverish and
with flu-like symptoms. A diagnosis of malaria is suspected. The form of the
malaria parasite which invades erythrocytes is known as a:

A Sporozite

B Schizont

C Merozite

D Hypnozoite

E Gametocyte

Answer 33

C Merozite

The merozites escape from the liver into the blood stream and infect
red blood cells – the erythrocytic phase

Question 34

A 55-year-old housewife returns from visiting her relatives in India, with a high
fever and with flu-like symptoms. A diagnosis of uncomplicated falciparum
malaria is confirmed. The most appropriate management plan is:

A Discharge with oral quinine and doxycycline

B Discharge with oral mefloquine and chloroquine

C Admit, give IV paracetemol and observe

D Admit and give IV quinine

E Admit and give oral quinine and doxycycline

Answer 34

E Admit and give oral quinine and doxycycline

Uncomplicated malaria can be treated with one of the following:
1 Oral quinine plus doxycycline for 5–7 days (E)
2 Co-artem (artemetherelumefantrine) for 3 days
3 Atovaquone–proguanil (Malarone) for 3 days

Question 35

A 55-year-old housewife returns from visiting her relatives in India, with a
high fever and with flu-like symptoms. thick and thin films are requested, and
Maurer’s clefts are seen under the microscope. The diagnosis is:

A Plasmodium falciparum

B Plasmodium vivax

C Plasmodium ovale

D Plasmodium malariae

E Plasmodium knowlesi

Answer 35

A Plasmodium falciparum

The most reliable way to diagnose malaria is via a blood film, and
traditionally a thick and thin blood film are requested. Most people
remember this fact, but not the reason behind it! Thick films are better
than thin films at picking up lower levels of infection, but thin films
allow the specific species to be identified. Both types of films are used
together to make the diagnosis.
In the erythrocytic life cycle of the malarial parasite, disc-like granulations
can be seen at the edge of the cell using an electron microscope.
These are known as Maurer’s clefts, and are found in falciparum malaria
(A).