Infectious Diseases

Question 1

Gram-negative, lactose-fermenting bacillus and a common cause of UTI.

Answer 1

E Coli.

(Responsible for 75-95% of UTI, but a normal commensal of large intestine. Transfer to urinary tract can be via bloodstream / lymphatics / direct extension e.g. vesicocolic fistula / ascending transurethral route most common - esp. in women).

Question 2

Gram-Positive, alpha-haemolytic diplococcus that causes lobar pneumonia.

Answer 2

Streptococcus pneumonias.

(90% of pneumonia due to Strep. pneumoniae. Colonies described as “draughtsman shaped” due to their sunken centre. Homeless and alcoholics with poor social/medical care are v prone to lobar pneumonia).

Question 3

Gram-positive, anaerobic, cytotoxin producing bacillus causing pseudomembranous colitis.

Answer 3

Clostridium difficile.

(Toxigenic strain. C diff produces two toxins: Toxin A - enterotoxin responsible for gut symptoms, Toxin B - cytotoxin with cytopathic effect in cell cultures).

Question 4

S-shaped urease-positive bacillus, major cause of chronic gastritis and peptic ulcer disease. Stains poorly with gram stain.

Answer 4

Helicobacter pylori.

H. pylori is a flagellate bacillus that produces urease and colonises the gastric antrum.

Question 5

Helicobacter pylori is associated with an increased risk of developing which conditions?

Answer 5

• Chronic gastritis.
• Duodenal ulcer.
• Gastric adenocarcinoma.
• Primary gastric lymphoma.

Question 6

How is Helicobacter pylori tested for?

Answer 6

• Serology for IgG antibodies.
• Urea breath test.
• Endoscopy: rapid urease test, microbiological culture, histological identification in gastric biopsy.

Question 7

How is Helicobacter pylori best visualised?

Answer 7

Modified Giemsa stain.

Question 8

Gram negative coliforms.

Answer 8

• E. Coli
• Klebsiella
• Enterobacter
• Proteus

Question 9

Which antibiotic are most gram negative coliforms and Pseudomonas aeruginosa sensitive to?

Answer 9

• Gentamicin.

- Aztreonam.

Question 10

Extended spectrum beta lactamases are resistant to most of which antibiotic?

Answer 10

Penicillins e.g. co-amoxiclav, piperacillin tazobactam, aztreonam.

Question 11

Which antibiotics do extended spectrum beta-lactamases have sensitivity to?

Answer 11

• Temocillin.
• Pivemcillinam.
• Meropenem.

Question 12

Anaerobes are generally sensitive to which antibiotics?

Answer 12

• Metronidazole.

- Co-amoxiclav, Clindamycin, Pip-tazobactam, Meropneme.

Question 13

Gram positives e.g. Staph aureus, Streptococci and Enterococci are sensitive to?

Answer 13

Vancomycin.

Question 14

Beta-haemolytic streps are sensitive to?

Answer 14

• Penicillin.

- Flucloxacillin.

Question 15

Which investigations are needed for infection of the CNS?

Answer 15

• Blood cultures.
• Bacterial and viral throat swabs.
• EDTA for bacterial PCR.
• CSF sample if safe to do so.

Question 16

Which organisms are likely to cause epiglottitis?

Answer 16

• Haemophilus influenza.

- Streptococci.

Question 17

Which organisms are likely to cause meningitis in someone >60 y/o?

Answer 17

Listeria, meningococcus, pneumococcus.

Question 18

Which investigations are needed for pneumonia?

Answer 18

• Blood cultures.
• Viral throat swab.
• Sputum for bacterial culture.
• BAL or tracheal aspirates if clinically indicated (PCR for legionella or PCP).

Question 19

Likely causative organism in someone with acute native valve endocarditis?

Answer 19

Staph. aureus.

Question 20

Likely causative organism in someone with subacute native valve endocarditis?

Answer 20

• Viridans streptococci.

- Enterococci.

Question 21

Likely causative organism in someone with prosthetic valve endocarditis?

Answer 21

• MRSA.

- Coagulase negative Staphylococci.

Question 22

What microbiology samples should be taken from someone with a central venous catheter related infection?

Answer 22

• blood cultures from peripheral site and the line using strict aseptic technique.
• Swab exit site if infected.

Question 23

Likely causative organism in someone with peritonitis / biliary tract sepsis / intra-abdominal infection?

Answer 23

• Polymicrobial coliforms.
• Anaerobes.
• Enterococci.

Question 24

Likely causative organism in someone with spontaneous bacterial peritonitis?

Answer 24

• Coliforms +/- anaerobes.

- Strep. pneumonia.

Question 25

Investigations in someone with suspected E. Coli 0157 infection?

Answer 25

• FBC, U+Es, LDH, CRP.

- Blood film (fragmented blood cells in HUS).

Question 26

Likely causative organism in a female with uncomplicated UTI?

Answer 26

• Coliforms.

- Enterococci.

Question 27

Likely causative organism in a male with UTI (not catheter related)?

Answer 27

• Coliforms.

- Enterococci.

Question 28

Likely causative organism in someone with complicated UTI / pyelonephritis urosepsis?

Answer 28

• Coliforms.
• Pseudomonas aeruginosa.
• Enterococci.

Question 29

Likely causative organism in someone with cellulitis?

Answer 29

• Staph. aureus.

- Group A and other beta-haemolytic Streptococci.

Question 30

Likely causative organism in someone with acute diabetic foot infection?

Answer 30

Staph aureus.

Question 31

Likely causative organism in someone with acute on chronic polymicrobial diabetic foot infection?

Answer 31

• Staph. aureus.
• Coliforms.
• Anaerobes.

Question 32

Why is Ceftriaxone used in CNS infections?

Answer 32

• Need for high CSF levels to be maintained.

- Easy dosing (twice daily).

Question 33

Listeria is resistant to X but sensitive to Y.

Answer 33

• X - Cephalosporin.

- Y - Amoxicillin.