DMF Week 2 SAQ

1

Select from the options below the site of action of Ampicillin


  cell wall

  protein synthesis

  nucleic acid

  folic acid metabolism

  cell membrane

2

Select from the options below the site of action of Gentamicin


  cell wall

  protein synthesis

  nucleic acid

  folic acid metabolism

  cell membrane

3

Select from the options below the site of action of Vancomycin


  cell wall

  protein synthesis

  nucleic acid

  folic acid metabolism

  cell membrane

4

Select from the options below the site of action of Trimethoprim


  cell wall

  protein synthesis

  nucleic acid

  folic acid metabolism

  cell membrane

5

Select from the options below the site of action of Cefotaxime


  cell wall

  protein synthesis

  nucleic acid

  folic acid metabolism

  cell membrane

6

Ms. S.J., aged 22 years, presented to her GP with a one day history of frequency and pain on passing urine. She had no fever and was not taking any medication. This was the third time she has had these symptoms within the past two years. The doctor examined her, and found no abnormalities. A urine dip-stick test was positive and suggested urinary infection and a midstream urine sample was sent for microbiological studies. Which one of the following organisms is the most likely cause of Ms. S.J.’s infection, assuming that she does have a UTI?


  Staphylococcus epidermidis

  Staphylococcus saprophyticus

  E. coli

  Proteus mirabilis

  Enterococcus faecalis


A is incorrect: S. epidermidis is a rare cause of UTI, typically seen in hospitalised patients. B is incorrect: However, S. saprophyticus is associated with 5 – 10% UTI, particularly in young, sexually active women. C is correct: E. coli is the most common cause of UTI, in both community acquired infection (around 80% cases) and hospitalised patients (around 40% cases). D is incorrect: Pr. Mirabilis causes around 6 – 11% of UTI in both outpatients (6%) and hospitalised patients (11%), especially in males. E is incorrect: Enterococci are rare causes of UTI, typically seen in hospitalised patients.

7

Resistance to penicillin in Streptococcus pneumoniae is due predominantly to which one of the following mechanisms?


  The ability of the organism to pump penicillin out of the cell

  The ability of the organism to block penicillin from entering the cell

  The ability of the organism to produce a beta-lactamase

  The ability of the organism to produce excess peptidoglycan

  The ability of the organism to mutate its penicillin binding proteins


Strep. pneumoniae does not produce beta-lactamases.

8

A young woman presented with a high fever, hypotension, a widespread erythematous rash and headaches and myalgia. She had started menstruating the day before she presented, and was using a vaginal tampon. Microbiological investigations suggested a diagnosis of toxic shock syndrome. Which one of the following statements is likely to be correct regarding this syndrome?


  The most likely causative organism is most typically carried in the vagina.

  The syndrome is only associated with infections in women.

  The syndrome is predominantly due to the release of toxins that target epithelial cells.

  The most likely causative organism is catalase positive and coagulase positive.

  The predominant virulence factor of the most likely causative organism is a capsule made of hyaluronic acid.


A is incorrect: The most likely causative organism is more commonly carried in the upper respiratory tract and skin. B is incorrect: Males and young children of both sexes may suffer from this disease. C is incorrect: The disease is due to the production of a superantigen which activates a significant number of T cells, inducing the release of their cytokines. D is correct: S. aureus is the most common cause of this condition. Str. pyogenes (catalase negative) may also produce a superantigen but is less commonly involved. E is incorrect: The most likely causative organism, S. aureus, produces a large number of virulence factors, toxic shock syndrome toxin, TSST-1, being the most important in this syndrome. Whilst some staphylococci do produce capsules which may contribute to their virulence, the capsules are predominantly polysaccharide.