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MI11.1-3 | Antimicrobial Resistance & Stewardship — PBL Case

CLINICAL SETTING

Madhav Medical College & Hospital, Nagpur — a 650-bed teaching hospital with a 16-bed Medical Intensive Care Unit (MICU). It is the middle of July, the height of the monsoon season, and the unit is running at 112% occupancy. In the past three weeks, the MICU microbiology surveillance programme has flagged five patients with bloodstream infections caused by carbapenem-resistant Klebsiella pneumoniae (CRKP). The Infection Control Officer, Dr. Priya Reddy, has convened an emergency meeting with the MICU team, a clinical microbiologist, and the hospital's antimicrobial stewardship pharmacist. You are a third-year MBBS student on your microbiology posting, invited to observe — and contribute to — the discussion.

Trigger 1: The Cluster

Patient 1 (Trigger): Mr. Ramesh Kulkarni, 64 years old, a retired railway officer with type-2 diabetes and hypertension, was admitted 12 days ago with community-acquired pneumonia. He was initially improving on co-amoxiclav. On day 8, he developed a fever spike to 39.8°C with a new-onset altered sensorium. Blood cultures drawn immediately grew Klebsiella pneumoniae. The susceptibility report: Ampicillin R, all cephalosporins R, piperacillin-tazobactam R, meropenem MIC 32 µg/mL (R), imipenem R. Susceptible only to colistin and tigecycline. The clinician notes this is the third such isolate from the MICU this fortnight. The microbiologist confirms by PCR: blaOXA-48 and blaNDM-1 are both present in this isolate.

DISCUSSION POINTS

  • What does it mean for an organism to be 'carbapenem-resistant'? Distinguish between resistance mediated by OXA-48 versus NDM-1 — do both mechanisms have the same effect on the range of available antibiotics?
  • Mr. Kulkarni was admitted with community-acquired pneumonia and was improving. How do you explain the development of a CRKP bloodstream infection on day 8? What is the likely source, and what hospital-related factors may have contributed?
  • The susceptibility report shows 'susceptible to colistin'. Before prescribing colistin, what specific information about its mechanism of action and toxicity profile would the prescribing team need to consider?
Click to reveal Trigger 2: The Investigation (discuss previous trigger first!)

Trigger 2: The Investigation

Dr. Reddy shares the MICU antibiogram for the past month: 62% of Klebsiella blood isolates are CRKP. Environmental swabs are collected from five surfaces in the MICU — the nurse station counter, two bedside monitors, a shared nebuliser stand, and the sink drain. Three of five swabs grow CRKP with an identical resistance profile. Whole-genome sequencing (WGS) of all patient and environmental isolates confirms they are clonal — the same sequence type (ST258), the plasmid-borne blaOXA-48 being horizontally transmitted. A review of antibiotic prescribing records for the month reveals: 78% of MICU patients received meropenem or imipenem at some point during their stay. In 55% of prescriptions, no blood culture was drawn before initiation. The mean duration of carbapenem use was 9.2 days; evidence-based guidelines recommend 5–7 days for most indications. Dr. Reddy asks the team: 'What are we doing that is feeding this outbreak?'

DISCUSSION POINTS

  • The WGS data shows the same clone in patient isolates and environmental surfaces. What does this tell you about the route of transmission? What specific IPC measures are urgently needed, and which of these is most likely to interrupt the outbreak?
  • How does the prescribing data (78% carbapenem use, 9.2-day mean duration, 55% no pre-treatment culture) contribute to the emergence and perpetuation of CRKP in this MICU? Use the concept of 'selection pressure' in your answer.
  • The plasmid carrying blaOXA-48 is transmissible. Explain the mechanism by which a new organism could acquire this resistance gene. What feature of plasmid biology makes this clinically alarming in an ICU setting?
Click to reveal Trigger 3: Management & Stewardship Response (discuss previous trigger first!)

Trigger 3: Management & Stewardship Response

Mr. Kulkarni develops septic shock. His renal function deteriorates (serum creatinine 3.4 mg/dL). The ID consultant recommends colistin plus high-dose meropenem (in a 'double-carbapenem' strategy) given the limited options. Colistin is initiated with careful monitoring for nephrotoxicity. In parallel, the AMSP team proposes an urgent stewardship package for the MICU: — Immediate restriction: all carbapenems and colistin require pre-authorisation from the ID team or AMSP pharmacist — 72-hour mandatory review of all broad-spectrum antibiotic prescriptions — Culture-before-antibiotic protocol: no broad-spectrum antibiotic without documented blood culture collection — Weekly antibiogram feedback to MICU physicians — Contact isolation for all CRKP-positive patients The medical superintendent approves the package. Within six weeks, new CRKP bloodstream infections in the MICU fall from five per fortnight to one per month.

DISCUSSION POINTS

  • The AMSP package produced measurable results in six weeks. For each of the five components listed, identify which AMSP strategy category it belongs to (preauthorisation restriction, prospective audit, culture-before-antibiotic, feedback, or IPC). Justify your classification.
  • Colistin nephrotoxicity is a major concern in a patient with already-elevated creatinine. How does this therapeutic dilemma — the last drug causing harm — reflect the broader consequences of antimicrobial resistance for patient care? What stewardship actions earlier in this admission might have prevented reaching this point?
  • As a future clinician in a district hospital in India with no ID specialist, which TWO elements of the AMSP package do you think are most feasible to implement independently, and why? What barriers might you face?

Group Task Assignments

Group 1: Resistance Mechanisms & Laboratory Interpretation

  • Prepare a visual summary (flowchart or table) distinguishing Class A (KPC), Class B (NDM, VIM), and Class D (OXA-48) carbapenemases: substrate range, inhibitor susceptibility, detection method, and treatment implications.
  • Using the mCIM/eCIM phenotypic test principle, explain how you would distinguish a class B MBL from a class D OXA-48 carbapenemase in the laboratory without PCR.

Competencies: MI11.1, MI11.2

Group 2: Epidemiology, Transmission & IPC

  • Map the likely transmission route for the MICU outbreak using the trigger data. Identify three specific IPC gaps and propose a surveillance protocol to detect new CRKP cases earlier.
  • Explain the concept of plasmid-mediated horizontal gene transfer. Using NDM-1 as an example, describe how resistance spread from a single hospital can reach national and global scale.

Competencies: MI11.2

Group 3: Antimicrobial Stewardship Design

  • Draft a one-page 'MICU Antibiotic Policy Card' for Ward 6 with first-line, second-line, and restricted-agent guidance for the three most common infection types (HAP/VAP, BSI, UTI) based on the antibiogram provided.
  • Role-play a 72-hour antibiotic review conversation: one student is the prescribing resident who started meropenem empirically; the other is the stewardship pharmacist reviewing on day 3 when culture shows susceptible E. coli. Demonstrate de-escalation communication skills.

Competencies: MI11.3

Learning Issues

Research these questions and bring your findings to the discussion.

  1. [MI11.1] How does the mCIM/eCIM test distinguish class B (MBL) from class D (OXA) carbapenemases phenotypically, and what are the treatment implications of each?
  2. [MI11.1] What is the mechanism of colistin's antibacterial action, and how does lipid A modification (mcr-mediated or chromosomal) confer resistance?
  3. [MI11.2] How does co-production of OXA-48 plus an ESBL eliminate the entire beta-lactam class for a single Klebsiella isolate?
  4. [MI11.2] What is ST258, and why is whole-genome sequencing important in outbreak investigation of drug-resistant organisms?
  5. [MI11.3] What are the five core AMSP strategies, and which are achievable in Indian district hospital settings without specialist support?
  6. [MI11.3] What evidence supports carbapenem prescription review at 72 hours as a stewardship intervention, and what clinical endpoints does it improve?