Microbiology

Question 1

4 mechanisms of antibiotic action and examples of each.

Answer 1

1. Inhibit cell wall synthesis: Penicillins, cephalosporins, glycopeptides: Co-amoxiclav, Pip/Taz, Cefuroxime, Ceftriaxone, Cefotaxime, Vancomycin & Teicoplanen
2. Inhibit DNA synthesis: Metronidazole, Rifampicin, Quinolones: Ciprofloxacin
3. Inhibit tetrahydrofolate synthesis: Trimethoprim, Co-trimoxazole
4. Inhibit protein synthesis: Tetracyclines, amino glycosides, macrolides, Clindamycin & Linezolid

Question 2

Mechanisms of anti-microbial resistance

Answer 2

1. Intrinsic: Lack of molecular target, lack of active transport mechanism & impermeability of membrane
2. Acquired: Drug inactivation (e.g. beta-lactamases), reduced permeability (loss of channels/ alteration), effluent of drugs (active transport out of cell), altered molecular target (low affinity penicillin binding protein in MRSA)

Question 3

How do bacteria acquire resistance?

Answer 3

1. Innate
2. Sporadic mutation
3. Gene transfer: Lysis of cells and release of free DNA, bacteriophages (viruses) that transfer DNA, plasmids, small segments of DNA that can move independently

Question 4

What is leptospirosis?

Answer 4

Leptospirosis is a disease caused by the genus of leptospira bacteria.
It is typically spread by the urine and faeces of infected animals - commonly rats.
It is a biphasic illness with a long incubation period with a septicaemic phase (characterised by fever, headache, myalgia, D+V; 5-7 days) and an immune phase (7-14 days later; characterised by conjunctival congestion, jaundice, renal failure, hepatosplenomegaly, haemorrhagic petechiae)
In the immune phase spirochetes are excreted in the urine.

Question 5

What are the common organisms implicated in community acquired pneumonia?

Answer 5

Strep pneumoniae
Mycoplasma pneumoniae
Chlamidya pneumoniae
Haemophilis influenzae
Staph aureus
Legionella pneumoniae

Question 6

How do you grade severity of CAP?

Answer 6

CURB-65 score

Confusion
Urea >7
Respiratory rate >30
BP <90/60
Age >65

0-1 = Mild = 30-day Mortality 1.2%
2 = Moderate = 30-day Mortality 9.5%
3-5 = Severe = 30-day Mortality 22%

Question 7

What organisms are commonly implicated in HAP?

Answer 7

Gram -ve organisms usually

Pseudomonas
E.coli
Klebsiella
Acinetobacter

Question 8

What can impact upon antibiotics in critical illness?

Answer 8

Absorption - gut oedema, impaired function, impaired splanchnic blood flow
Distribution - oedema, extracorporeal circuits, reduced proteins, acid-base derangement
Metabolism - hepatic impairment
Excretion - Biliary obstruction, renal impairment

Question 9

What are the three dosing patterns of antibiotics?

Answer 9

Concentration dependent = Cmax:MIC e.g. aminoglycosides, metronidazole (bonus regimes)
Time dependent = T>MIC e.g. penicillins, linezolid, clindamicin (frequent dosing or continuous infusion)
Concentration and time dependent = MIC:AUC e.g. quinolones

Question 10

What is PVL?

Answer 10

Paton Valentine Leukocidin is a cytotoxin associated with Staph aureus infection that creates pores in the membranes of infected cells

Features of PVL infection include skin lesions, pulmonary haemorrhage, leukopenia
Cause of necrotising pneumonia, nec fasc., osteomyelitis
Risk factors include compromised skin integrity, sharing of contaminated items, contact sports, gyms, prisons
Management focus on wound hygiene, I+D of collections, debridement of infected tissue
Antibiotics: PHE suggest 1. Linezolid + Clindamycin; 2. IVIg and Rifampicin

Question 11

What are the HACEK organisms

Answer 11

Haemophilus
Acintobacillus
Cardiobacterium hominus
Eikenella corrodens
Kingella kingae

All gram negative