MI11.1-3 | Antimicrobial Resistance & Stewardship — Graded Quiz

A tertiary-care hospital's antibiotic stewardship team reviews an unusual antibiogram: a Klebsiella pneumoniae isolate from a bloodstream infection is sensitive to aztreonam but resistant to all carbapenems, including imipenem and meropenem. The isolate tests positive for a metallo-beta-lactamase (MBL). Which property of aztreonam explains its retained activity against MBL-producing organisms?

A 58-year-old diabetic man is admitted to a Chennai hospital with a necrotising soft-tissue infection of the right foot. Wound swab culture grows Pseudomonas aeruginosa with the following MIC results: piperacillin-tazobactam 32 µg/mL (R), ceftazidime 8 µg/mL (S), imipenem 4 µg/mL (S), and ciprofloxacin 2 µg/mL (R). The infectious disease team notes that after 48 hours of ceftazidime therapy, repeat culture shows full resistance (MIC >64 µg/mL) to all cephalosporins. Which mechanism BEST explains this in-vivo resistance development?

A hospital infection-control nurse audits antibiotic prescriptions in a 40-bed medical ward over one month. She finds that 70% of prescriptions for community-acquired pneumonia use meropenem empirically, whereas the national treatment guideline recommends amoxicillin-clavulanate plus a macrolide. The stewardship pharmacist proposes an 'antibiogram-guided formulary restriction' intervention. Which stewardship strategy does this BEST exemplify?

A 72-year-old woman post-hip replacement develops a surgical site infection. Wound culture grows MRSA. The junior resident prescribes vancomycin 1 g IV every 12 hours. On day 3, the vancomycin MIC is reported as 2 µg/mL. The attending physician is concerned about 'MIC creep'. What does vancomycin MIC creep represent and what is its clinical significance?

A microbiology laboratory receives a rectal swab from a patient admitted to a medical ICU with a history of recent hospitalisation in Southeast Asia. Culture grows a Gram-negative rod that is resistant to all penicillins, cephalosporins, and carbapenems. The modified Carbapenem Inactivation Method (mCIM) is positive. EDTA inhibition restores susceptibility, and the isolate tests PCR-positive for blaVIM. What class of carbapenemase has been identified, and what is the key clinical implication?

The medical superintendent of a 300-bed district hospital in Maharashtra receives a report that Klebsiella pneumoniae bloodstream infection mortality has risen from 12% to 28% over two years, coinciding with increased carbapenem use. A microbiologist proposes implementing a bundle: (1) review of all carbapenem prescriptions at 72 hours, (2) mandatory culture before antibiotic start, (3) restricted prescribing list for broad-spectrum agents. Which framework for AMSP does this bundle align with?

A clinical microbiology resident is interpreting zone-of-inhibition measurements for a Gram-negative isolate. For cefotaxime, the zone diameter is 24 mm. The CLSI breakpoints are: susceptible ≥26 mm, intermediate 23–25 mm, resistant ≤22 mm. A double-disk synergy test shows enhanced inhibition between a cefotaxime disk and an amoxicillin-clavulanate disk. What is the correct interpretation and its clinical implication?

A 55-year-old man with type-2 diabetes develops a non-healing foot ulcer. Wound swab culture grows mixed flora including Enterococcus faecium resistant to ampicillin, gentamicin (high-level), and vancomycin. Linezolid is reported as susceptible. Before prescribing linezolid, the treating physician must consider its mechanism of action. Which statement about linezolid's antibacterial mechanism is CORRECT?

An AMSP pharmacist audits antibiotic prescriptions in a surgical ICU. She finds that post-operative patients are routinely receiving piperacillin-tazobactam for 7 days as 'surgical prophylaxis'. Published data indicate that short-course (24 hours) prophylaxis is equivalent to prolonged courses for most clean-contaminated procedures. The primary concern with prolonged prophylactic antibiotic courses in the ICU is:

A microbiologist receives a sputum culture from a ventilated patient in the PICU showing Acinetobacter baumannii. The sensitivity report shows the isolate is susceptible only to colistin (polymyxin E) and tigecycline. Colistin is ordered. The medical officer asks the pharmacist about colistin's mechanism of action and the basis of resistance. Which statement is CORRECT?

A medical intern in a government hospital in Tamil Nadu wants to prescribe antibiotics for a patient with productive cough, fever (38.4°C), and lobar consolidation on chest X-ray. Before prescribing, she checks the hospital's antibiogram, which shows 82% S. pneumoniae susceptibility to amoxicillin and 45% susceptibility to azithromycin. She prescribes amoxicillin. The AMSP team commends her approach. Which stewardship behaviour did she PRIMARILY demonstrate?

A hospital stewardship team notes a cluster of five patients in an oncology ward with pan-resistant Klebsiella pneumoniae harbouring both an OXA-48 carbapenemase and a co-produced ESBL. The infection control nurse wants to understand why this combination makes therapeutic options so limited. Which property of OXA-48, when combined with an ESBL, makes this isolate particularly difficult to treat?