DMF MSE 1 2007

1

Which ONE of the following features distinguishes bacterial cells from eukaryotic cells most reliably?


  The presence of flagella on bacterial cells

  The presence of peptidoglycan in bacterial cells

  The absence of ribosomes from the cytoplasm of bacterial cells

  The presence of 16S rRNA in bacterial cells

  The susceptibility of bacterial cells to antibiotics

2

Which ONE of the following statements about exotoxins is INCORRECT?


  The mechanism of action of exotoxins varies, but in all cases their toxicity ends with the death of the host cell

  A - B exotoxins must bind to a receptor on the surface of the host cell before being able to induce damage

  Injection of tetanus and diphtheria toxoids into humans typically leads to the production of antibodies that neutralise the corresponding toxin

  Shiga toxin binds to its target cells, is endocytosed and following release of the Asubunit, blocks protein synthesis

  Cholera toxin binds enterocytes, is endocytosed, and following release of the active subunit, activates adenylate cyclase

3

Which ONE of the following statements about endotoxins is CORRECT?


  Endotoxins are synthesised in the cytoplasm of Gram negative bacteria, and are secreted as part of the metabolic process

  Endotoxins are part of the cell wall of both Gram positive and Gram negative bacteria, and are released when the bacteria die

  Endotoxins act by being internalised by target cells to induce cell death

  Endotoxins may be found in sterile solutions

  The toxic activity of endotoxins can be neutralised by antibodies directed against the polysaccharide “O” antigens associated with the molecule

4

Which ONE of the following statements about capsules is INCORRECT?


  Capsules can protect bacteria from phagocytes by electrostatic repulsion and/or hydrophobic/hydrophilic interactions

  The capsules of group A streptococci and group B meningococci protect the bacteria from phagocytosis because they are poorly antigenic

  The polysaccharide capsules of Streptococcus pneumoniae, Neisseria meningitidis and Haemophilus influenzae have been used to manufacture vaccines that prevent infections with these bacteria

  Capsules of Gram negative bacteria may mask pathogen-associated molecular patterns (PAMPs) on the bacterial surface, thus concealing the bacteria from the innate immune system

  When injected into animals, the capsules of Gram negative bacteria, such as E. coli, typically produce fever and shock

5

A pregnant pig was immunised with K88 fimbriae from an enterotoxigenic strain of E. coli (ETEC). Another pregnant pig was left unimmunised. Each sow gave birth to 16 piglets, eight of which were immediately given to the other pig to suckle (breast feed). After six days the piglets were inoculated with one of two different ETEC strains. One strain carried the K88 antigen on its fimbriae, and the other carried K99, an antigenically different type of fimbriae.

The number of piglets with diarrhoea / number inoculated is shown in the table below.

Which ONE of the following conclusions about the experiment is CORRECT?


  The K88 bearing strain of ETEC is significantly more virulent than the K99 strain

  E. coli which possess fimbriae typically cause diarrhoea

  Specific immunity to ETEC is transferred via breast milk/colostrum in pigs

  Specific immunity to ETEC can be transferred across the placenta in pigs

  It is not possible to vaccinate piglets against the K99 strain of ETEC

6

You have set up a solid phase assay to determine the presence of IgM antibodies to rubella virus in a pregnant woman.

Which of the reagents listed below is the FIRST reagent you would attach to the wells of a micro-titre tray, if the second reagent was the patient’s serum, the third reagent was rubella antigen, the fourth reagent was enzyme labelled anti-rubella immunoglobulin, and the final reagent was the enzyme’s substrate?


  Anti-rubella IgG

  Anti-human IgG

  Anti-human IgM

  Anti-human antibodies

  Anti-rubella virus antibodies

7

Which ONE of the following statements regarding the clinical importance of bacterial plasmids is CORRECT?


  The main function of bacterial plasmids is to transmit genes which code for resistance to antibiotics

  Transmission of genetic material via bacterial plasmids can only occur between related bacterial species

  Bacterial plasmids mutate rapidly and hence often carry genes for antibiotic resistance

  Acquisition of certain plasmids may make a bacterium more virulent

  Bacterial plasmids are spread by bacteriophages which replicate very efficiently to achieve large numbers

8

Gram positive cocci have developed several strategies to enable resistance to antibiotics that act on peptidoglycan synthesis, such as the beta-lactam and glycopepetide groups of antimicrobials.

Which ONE of the following is NOT KNOWN to be one of the resistance strategies to either penicillin G or vancomycin?


  Enzyme-mediated hydrolysis of beta-lactam

  Failure to activate an inactive form of vancomycin

  Production of increased amounts of peptidoglycan

  Reduction of the binding affinity of the antimicrobials to penicillin-binding proteins

  Replacement of terminal D-Ala-D-Ala with D-Ala-D-Lac

9

Which ONE of the following the BEST describes the mechanism of action of clavulanic acid?


  It binds to penicillins in such a way that they cannot be recognised by betalactamases produced by penicillin-resistant bacteria

  It binds irreversibly to some types of beta-lactamase to inhibit their action

  It binds to penicillin-binding proteins to interfere with their normal function

  It binds to terminal D-Ala–D-Ala to interfere with the synthesis of the bacterial cell wall

  It acts synergistically with other beta-lactam antibiotics, such as amoxycillin, by blocking the next stage in peptidoglycan synthesis

10

In a suspected outbreak of infection with enterohaemorrhagic E. coli (EHEC), which ONE of the following will NOT be useful in determining if EHEC isolates obtained from different patients are related?


  Determination of the O:H serotype

  Determination of their susceptibility to specific bacterial viruses (phage type)

  Determination of the DNA fingerprint by investigation of restriction fragment length polymorphism

  Investigation for the presence of particular virulence determinants

  Comparison of the nucleotide sequence of 16S rRNA/rDNA

11

Select the site from where you would be MOST LIKELY to isolate Pseudomonas aeruginosa:


  Oropharynx

  Skin

  Genital tract

  Soil

  Water

12

Which ONE of the following statements about innate immunity is INCORRECT?


  Neutrophils and natural killer cells contribute to innate immunity

  Cells of the innate immune system possess receptors that discriminate between individual pathogens

  Cells of the innate immune system possess receptors that recognise damaged cells

  Cells of the innate immune system possess receptors whose ligation triggers anti-viral responses

  Innate immunity plays an important role in protection against microorganisms not previously encountered by the host

13

Delegates at a Microbiology Society meeting attended the first night cocktail party where they were provided with sandwiches and other finger foods, and alcoholic and non-alcoholic drinks. However, 3 – 4 hours later around one quarter of those at the party developed severe abdominal cramps, nausea and profuse vomiting; a small number of those affected also developed diarrhoea.

Which ONE of the following microorganisms is the MOST likely to be associated with these symptoms?


  Campylobacter jejuni

  Enterotoxigenic E. coli

  Salmonella typhimurium

  Staphylococcus aureus

  Vibrio cholerae

14

Mrs G.B., aged 25 yrs, presents with a two day history of frequency and dysuria. She has no relevant past medical history or allergies, and is not taking any medications, apart from an oral contraceptive. She had these symptoms one month ago, when she had just returned from her honeymoon, but they resolved after the doctor she visited gave her some medication.

Which ONE of the statements below would be MOST consistent with the diagnosis of urinary tract infection?


  The isolation of 103 E. coli / ml in a mid-stream sample of urine, together with <104 neutrophils and epithelial cells / ml

  The isolation of 2 X 105 / ml E. coli and 105 Staphylococcus epidermidis in a midstream sample of urine, together with 105 neutrophils and 105 epithelial cells / ml

  The isolation of 105 Staphylococcus saprophyticus / ml in a mid-stream sample of urine, together with 105 neutrophils/ ml and <104 epithelial cells / ml

  The findings that she had a fever of 38.9°C and dysuria

  Her recovery following treatment with co-amoxyclav

15

Two months after surgery to place a prosthetic heart valve, Mr. A.F presented with symptoms suggestive of endocarditis. Blood cultures were collected and sent for microbiological examination. 24 hours later, the laboratory reported that a coagulase negative staphylococcus had been grown from the blood cultures. Antimicrobial susceptibility testing suggested that the organism was susceptible to methicillin.

Which ONE of the following statements is CORRECT?


  The organism grown by the laboratory is most likely to be Staphylococcus aureus

  The patient should be treated with high doses of vancomycin for 4 to 6 weeks

  The patient should be treated with high doses of flucloxacillin for 4 to 6 weeks

  After recovery, the patient should be maintained permanently on low doses of penicillin to prevent recurrences of infection

  The organisms which cause endocarditis usually produce toxins which damage the myocardium

16

One hundred and fifty persons who live in the City of Yarra were diagnosed with Chlamydia trachomatis urogenital infection during March 2004. Typically, approximately 360 persons from this Local Government Area are diagnosed with this infection in the course of each year.

Which one of the following is an UNLIKELY explanation of the above finding?


  A simple and sensitive new diagnostic method was recently introduced at the local pathology service.

  This is not a significant deviation from the expected number of cases.

  A local newspaper ran a series of articles during February on the failure of doctors to screen at-risk patients for chlamydia.

  Active screening of persons attending “sex-on-premises” venues in inner Melbourne was undertaken during March.

  A test that diagnoses the infection from a urine sample (rather than a genital swab) was approved for health insurance reimbursement.

17

The following steps are important parts of a typical outbreak investigation conducted by a State Health Department.

A: Analyse data by time, place, person and pathogen
B: Conduct a case-control study
C: Confirm that the number of cases exceeds the expected number
D: Conduct surveillance for additional cases
E: Generate hypotheses for an analytic epidemiological study
F: Verify the diagnosis of some cases

In what order should the activities listed above be conducted?


  C-E-B-D-A-F

  E-B-C-D-F-A

  C-F-D-A-E-B

  C-D-F-B-E-A

  F-D-E-A-C-B

18

For Clostridium perfringens food poisoning, the minimum incubation period is 8 hours, and average incubation period is 10 to 12 hours. Based on the graph below, when were most cases probably exposed to the contaminated food?


  Between 0600 and 1000 6 October

  Between 1000 and 1400 6 October

  Between 1400 and 1800 6 October

  Between 1800 and 2200 6 October

  Between 2200 6 October and 0200 7 October

19

Which of the following BEST describes the difference between an adverse event and an adverse outcome?


  There is no difference

  An adverse event is immediate; an adverse outcome is long term

  An adverse event is harm occurring to a patient; an adverse outcome is harm occurring to the doctor

  An adverse event is harm occurring to a doctor; an adverse outcome is harm occurring to the patient

  An adverse outcome is harm occurring to a patient; an adverse event is an event which exposes a patient to harm

20

Which ONE of the following statements about adverse outcomes is CORRECT?


  Patients think saying "Sorry" is an admission of liability

  Patients want to know what happened more than who did it

  Patients aren't interested in what you've learned

  Litigation rates are a measure of poor quality

  Adverse events always result from negligent acts

21

Which ONE of the following questions is an "open ended" question?


  Tell me about your problem today?

  Is the pain in your abdomen as well?

  Do you have children?

  Do painkillers relieve the pain?

  Are you allergic to medications?

22

When taking a patient history, which ONE of the answers below BEST describes the activating trigger for the patient's chest pain?


  It feels like a crushing chest pain

  It has lasted for about 3 hours

  The pain improves when I rest

  I also notice shortness of breath

  I noted the pain started with me walking up the hill