Page 4 of 7
MI11.1-3 | Antimicrobial Resistance & Stewardship — Practice Quiz
Practice
10 questions · Untimed · Unlimited attempts
Click any question card to reveal the correct answer.
A clinical laboratory uses the Kirby-Bauer disk diffusion method to test antibiotic susceptibility. The Mueller-Hinton agar plate is incubated for 16–18 hours, and the zones of inhibition are measured. According to CLSI breakpoints, a zone diameter of 12 mm for ampicillin is interpreted as 'Resistant' for E. coli. What is the primary mechanism being assessed by this test?
A
Whether the organism can enzymatically destroy the antibiotic in the disc before it diffuses
B
The ability of the antibiotic to diffuse through agar and inhibit visible bacterial growth around the disc
✓
C
Measurement of the minimum concentration that kills 99.9% of organisms
D
Detection of specific resistance genes by hybridisation with the disc substrate
Click to reveal answer
A first-year resident orders a blood culture for a patient with suspected sepsis. The result shows Pseudomonas aeruginosa. The susceptibility report lists imipenem as 'Susceptible' but notes that the isolate may carry an inducible AmpC beta-lactamase. Which resistance mechanism underlies inducible AmpC beta-lactamase-mediated resistance in Pseudomonas aeruginosa?
A
Acquisition of a plasmid encoding a carbapenemase enzyme
B
Chromosomally encoded cephalosporinase that can be de-repressed by exposure to certain beta-lactams
✓
C
Alteration of penicillin-binding proteins reducing antibiotic affinity
D
Overexpression of efflux pumps exporting all classes of antibiotics equally
Click to reveal answer
A 68-year-old man with a urinary catheter in an ICU develops a UTI. Urine culture grows Klebsiella pneumoniae resistant to all third-generation cephalosporins but susceptible to imipenem. The lab reports the isolate is ESBL-producing. What is the most likely mechanism of resistance responsible for cephalosporin resistance in this isolate?
A
Loss of outer membrane porins reducing drug uptake
B
Production of extended-spectrum beta-lactamases that hydrolyse the oxyimino side chain of 3rd-generation cephalosporins
✓
C
Upregulation of efflux pumps exporting cephalosporins extracellularly
D
Alteration of PBP3 reducing cephalosporin affinity
Click to reveal answer
During morning rounds in a medical ward, a house officer prescribes a 14-day course of broad-spectrum antibiotics for a patient with a mild community-acquired urinary tract infection caused by susceptible E. coli. The attending physician reviews the prescription. Which principle of antimicrobial stewardship is MOST directly violated by this prescription?
A
Choosing the right antibiotic based on culture and sensitivity
B
Prescribing the right duration — using the shortest effective course to prevent resistance selection
✓
C
Using the correct route of administration (oral vs. intravenous)
D
Documenting the indication for the antibiotic in the medical record
Click to reveal answer
A microbiologist interprets a susceptibility report for a Staphylococcus aureus isolate. The MIC for oxacillin is 4 µg/mL. The CLSI breakpoint for oxacillin susceptibility in S. aureus is ≤2 µg/mL. What does this result indicate, and what is the underlying mechanism?
A
The isolate is susceptible; the MIC is within acceptable therapeutic range for standard dosing
B
The isolate is MRSA; the mecA gene encodes PBP2a, which has very low affinity for all beta-lactams
✓
C
The isolate produces beta-lactamase that destroys oxacillin before it reaches the target
D
The isolate is resistant only to oxacillin but remains susceptible to all other penicillins
Click to reveal answer
Carbapenem-resistant Klebsiella pneumoniae (CRKP) is isolated from a wound swab in a tertiary care ICU in India. The isolate tests positive for the NDM-1 (New Delhi Metallo-beta-lactamase-1) gene by PCR. Which of the following correctly describes NDM-1?
A
A serine-based enzyme encoded on the chromosome that destroys all beta-lactams except aztreonam
B
A zinc-dependent metallo-beta-lactamase carried on transferable plasmids, conferring resistance to carbapenems and all beta-lactams except aztreonam
✓
C
An efflux pump inhibitor that excludes carbapenems from the bacterial periplasm
D
A modified penicillin-binding protein encoded on the chromosome, similar to PBP2a in MRSA
Click to reveal answer
A hospital antibiotic stewardship committee reviews prescribing data and finds that 65% of all surgical prophylaxis regimens exceed 24 hours. The infectious disease physician on the team proposes a 'de-escalation' strategy. What does de-escalation mean in antimicrobial stewardship?
A
Stopping all antibiotics after the first 24 hours regardless of the clinical picture
B
Switching from broad-spectrum empiric therapy to a narrower-spectrum targeted agent once culture data and clinical improvement are available
✓
C
Reducing the dose of the antibiotic by 50% once the patient stabilises
D
Replacing intravenous antibiotics with oral agents for all patients after 48 hours
Click to reveal answer
Vandana, a 32-year-old woman, is admitted to hospital with uncomplicated right lower lobe pneumonia. She is started on ampicillin-sulbactam. Culture of sputum grows Streptococcus pneumoniae susceptible to penicillin. The attending physician changes her antibiotic to amoxicillin. Which stewardship strategy does this change BEST exemplify?
A
Formulary restriction — limiting the formulary to beta-lactam antibiotics only
B
De-escalation — narrowing from a beta-lactam/beta-lactamase inhibitor combination to a simpler targeted penicillin
✓
C
Dose optimisation — adjusting the dose based on pharmacokinetic/pharmacodynamic principles
D
Automatic stop orders — mandating review at 48 hours by hospital policy
Click to reveal answer
Which of the following statements correctly describes an INTRINSIC resistance mechanism — one that is naturally present in the species without requiring prior antibiotic exposure or gene acquisition?
A
Staphylococcus aureus producing penicillinase (beta-lactamase) to destroy penicillin
B
Pseudomonas aeruginosa being naturally resistant to most first-generation cephalosporins due to low outer membrane permeability and intrinsic efflux pumps
✓
C
Klebsiella pneumoniae acquiring an NDM-1 plasmid from another organism in the ICU environment
D
Mycobacterium tuberculosis developing rifampicin resistance by mutation in the rpoB gene during inadequate monotherapy
Click to reveal answer
A medical student rotating in microbiology is asked to interpret an antibiogram for a hospital ICU. She notices that for Acinetobacter baumannii, all third-generation cephalosporins, fluoroquinolones, and carbapenems are listed as 'Resistant'. Only colistin and tigecycline show 'Susceptible'. Which ESKAPE pathogen property does this antibiogram pattern BEST illustrate?
A
Intrinsic resistance to carbapenems, present since the genus first appeared
B
Simultaneous deployment of multiple acquired resistance mechanisms — beta-lactamases, efflux pumps, and porin loss — leading to pan-drug resistance
✓
C
Resistance driven exclusively by mecA-mediated PBP alteration, similar to MRSA
D
Loss of all virulence factors, allowing the organism to survive but not cause true infection
Click to reveal answer