mmb_e_2003 by nuhman10


									Medical Microbiology B (CXA 343)                            Final Examination 2003

           Medical Microbiology B (CXA 343)

               Final Theory Examination 2003
                           Deferred Paper

                         Examiner Mr Stephen Tristram

There are seventeen (17) questions worth a total of 180 marks.


   Students are to attempt all questions – there are no choices.
   Answer all questions in the examination booklets.
   Record your student identification number on all answer booklets.
   Please indicate on the front of each answer booklet (in order) which
    answers are contained within them.
   You are encouraged to include diagrams if they enhance your answer.
   You MAY NOT keep the paper at the end of the examination.

Medical Microbiology B (CXA 343)                            Final Examination 2003

Question 1 (5 marks)

What are the typical macroscopic (briefly describe) and microscopic features
(please illustrate) of fungi that belong to the family Zygomycetes? List two (2)
genera from this family.

Question 2 (5 marks)

Briefly describe the habitat, types of disease, atmospheric requirements in
culture, colonial morphology and microscopic morphology of the collection of
organisms commonly referred to as “actinomycetes”. List two (2) genera.

Question 3 (10 marks)

You are a senior scientist in a laboratory and a junior who is examining a
faecal wet preparation on x 40 phase contrast, calls you over to look at
something and offer some advice. When you sit down to view the preparation,
the image quality is terrible. What aspects of the microscope set up will you
check and or adjust to try and improve the image quality?

Question 4 (5 marks)

In infants with diarrhoea, it is not uncommon for a clinician to request a test
for "faecal reducing substances".

What is this test, and what is the possible connection with the diarrhoea?

What is the most common cause of false negative results with this test? Briefly

Question 5 (5 marks)

You have a culture of a dermatophyte that you suspect is M. gypseum. On
Sabourauds agar after three weeks incubation you have a tan coloured flat
granular powdery thallus about 3 cm in diameter with a 1cm diameter central
white fluffy raised section.

Microscopy of the central area shows only sterile septate hyphae. What will
you do now?

Medical Microbiology B (CXA 343)                           Final Examination 2003

Use a simple labelled line drawing to illustrate the typical microscopic features
of M. gypseum.

Medical Microbiology B (CXA 343)                          Final Examination 2003

Question 6 (10 marks)

You receive a stool specimen from a patient with chronic diarrhoea and
flatulence and the requesting doctor is convinced that the patient has

You prepare a standard direct saline wet preparation of the stool and examine
it under the x40 objective but cannot see any Giardia.

What additional tests/procedures would you recommend or perform to try
and establish or exclude giardiasis as a diagnosis?

Question 7 (5 marks)

What type of disease do you associate with Pneumocystis carinii, and how is it

Question 8 (10 marks)

A clinician contacts you for advice about a patient suspected of having
amoebic dysentery (Entamoeba histolytica infection).

What advice will you provide regarding the collection of a stool specimen?

How will you handle the specimen, what tests will you perform and what
microscopic details will you need to observe to identify the organism (and
differentiate it from a similar non pathogen) if it is present?

Question 9 (5 marks)

Trichophyton rubrum and Trichophyton mentagrophytes are the two
dermatophytes most commonly isolated from human specimens.

With the aid of labelled diagrams, describe the typical microscopic
characteristics of each organism.

Question 10 (10 marks)

Various agar “schemes” have been devised to assist in the identification of
dermatophytes. Two such schemes are the “Trichophyton agar scheme”, and
the “Kaminski agar scheme”.

Medical Microbiology B (CXA 343)                                  Final Examination 2003

Briefly describe how and when these schemes would be used in the process of
dermatophyte identification. Compare them in terms of usefulness in
identifying dermatophytes in a routine laboratory.
Note that it is not necessary to describe the composition of the agars in detail to answer
the question.

Medical Microbiology B (CXA 343)                            Final Examination 2003

Question 11 (10 marks)

The complete microbiological analysis of most specimens is usually best
achieved with a combination of direct microscopy on the specimen, in
conjunction with culture. In many cases, much of the value of the direct
microscopy is in the fact that it provides more rapid results than culture.

In infections involving Aspergillus species, direct microscopy is often more
important than with other organisms.

This additional importance is unlikely to be due to the speed with which a
result can be obtained. Why?

So what is the real value of direct microscopy on specimens from which
Aspergillus is subsequently isolated?

Question 12 (10 marks)

What are the three most common species of Aspergillus isolated from clinical

What laboratory observations are useful in determining the species of
Aspergillus isolated in culture? (Note that it is not necessary to list how each
feature might appear specifically for each species).

Question 13 (15 marks)

Cryptosporidium is an important cause of diarrhoea but the parasite cannot be
reliably detected in a standard saline preparation of stool.

Describe two different techniques that can be used for the microscopic
detection of the stool with a standard light microscope. Describe the
appearance of the oocysts using the different methods and briefly discuss the
other organisms that might be confused with the “real thing”. How can such
false positives be avoided?

Compare the two methods in terms of sensitivity, specificity, convenience and

Medical Microbiology B (CXA 343)                            Final Examination 2003

Question 14 (15 marks)

Briefly describe / illustrate the normal diagnostic stage seen in faeces for
infection with Strongyloides stercoralis and for hookworm.

If you saw both of these parasitic forms in the same specimen what would
be\the possible explanations and what additional observations might assist
you in making a diagnosis?

Medical Microbiology B (CXA 343)                          Final Examination 2003

Question 15 (15 marks)

A patient has come to the laboratory at Launceston Pathology complaining of
vague symptoms including tiredness and chronic but intermittent diarrhoea
and abdominal pain. These symptoms have been present for about 4 months
which roughly coincides with the patient's return from a trekking holiday
across Asia.

A range of tests have been requested including a full blood count and a stool

During your examination of a standard direct saline stool wet preparation you
immediately detect some parasites and some crystals (see fig1). There are
approximately 10 of the variably sized parasites per high power x40 field and
about 30 of the crystals.

What are the parasites and crystals, and what are the possible connections
between their presence and the patient's symptoms?

What additional procedures might you perform on the stool specimen, and
what other samples (if any) might you request?

                                  Fig 1

Medical Microbiology B (CXA 343)                           Final Examination 2003

Question 16 (25 marks)

A patient has arrived at the laboratory with a request form requesting the
investigation of onychomycosis of the nail of the big toe. On examination the
nail is brown and dystrophic.

For the purposes of this question, confine your answer to mycological

a) Explain how you will collect the specimen.

b) Which organisms might you suspect?

c) Would the presence or absence of associated tinea around the contiguous
skin influence the possible range of fungal pathogens? Explain.

d) How would you go about performing direct microscopy on the specimen,
and what results might you see for some of the possible causes listed above?
Use simple diagrams to enhance your answer.

e) In terms of sensitivity, how does the performance of direct microscopy
compare with culture in the diagnosis of onychomycosis? Is the direct
microscopy in this instance more or less important than it is with the diagnosis
of tinea in other tissues?

f) Supposing you had only managed to collect a small amount of specimen and
following direct microscopy (which was positive) there was only enough left
to culture on one single medium. Which medium would you choose, and what
factors would you consider in your choice?

Medical Microbiology B (CXA 343)                           Final Examination 2003

Question 17 (25 marks)

A patient presents to her doctor because she is worried that she may have been
exposed to rubella when she visited a friend who apparently had the disease
at the time of the visit (which was 1 week ago). The patient is 12 weeks
pregnant and has suddenly felt as though she has the flu and is lethargic with
joint pains. She has a slight rash all over the body which developed on the
morning she saw the doctor.

In each of the different scenarios below you are provided with rubella serology
results from tests done 14 weeks ago as part of her antenatal screen (spec 0),
results from a specimen taken at this visit (spec 1) and a specimen taken in two
weeks time (spec 2). Specimen 1 was re-tested when specimen 2 was tested,
and the results were the same as when specimen 1 was initially tested.

For each scenario, describe and very briefly explain what the total set of
results mean in terms of a) her immune status to rubella at the time of
exposure, b) actual status now with respect to rubella infection, c) implications
for this pregnancy and d) suggested actions at the end of the pregnancy.

In some of the scenarios, you may want to do additional or repeat serology. If
so, briefly explain why.

To make this easier to mark, and to MAXIMISE reward for your effort, answer
in order, addressing points a) to d) fro each scenario.

    Scenario    Specimen 0         Specimen 1               Specimen 2
1              IgG ND         IgG ND / IgM Pos        IgG 125 / IgM Pos
2              IgG ND         IgG ND / IgM Neg        IgG 125 / IgM Pos
3              IgG 8          IgG 125 / IgM Pos       IgG 250 / IgM Pos
4              IgG ND         IgG ND / IgM Neg        IgG ND / IgM Neg
5              IgG 50         IgG 50 / IgM Pos        IgG 125 / IgM Pos
6              IgG ND         IgG ND / IgM Neg        IgG ND / IgM Pos

ND = not detected, numbers refer to IU/ml.


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