Carbapenem-Resistant Klebsiella pneumoniae in an Intensive Care Patient
A 71-year-old man has been in the intensive care unit for 10 days after emergency laparotomy. He develops fever of 38.9 °C, hypotension requiring noradrenaline, and worsening oxygenation. Two sets of blood cultures are taken. At 14 hours, one aerobic bottle from the peripheral set shows Gram-negative rods; the other three bottles remain negative at 5 days. The isolate identifies as Klebsiella pneumoniae. Automated susceptibility testing gives meropenem MIC 16 mg/L, imipenem MIC 8 mg/L, ertapenem MIC 4 mg/L, ceftazidime-avibactam MIC 2/4 mg/L, colistin MIC 1 mg/L, tigecycline MIC 1 mg/L, and amikacin MIC 32 mg/L. The laboratory routinely reports every antimicrobial on its panel. Infection prevention asks whether the patient needs a single room. The laboratory has mCIM/eCIM and a multiplex PCR for blaKPC, blaNDM, and blaOXA-48.
1. Interpret the susceptibility profile and decide what should be reported and what should be suppressed or confirmed.
Read the worked answer
Using current CLSI or EUCAST breakpoints for Enterobacterales, meropenem MIC 16 mg/L, imipenem MIC 8 mg/L, and ertapenem MIC 4 mg/L are all resistant, so this is a carbapenem-resistant Klebsiella pneumoniae. Ceftazidime-avibactam at 2/4 mg/L is susceptible, colistin at 1 mg/L is susceptible or intermediate depending on the breakpoint system, and tigecycline at 1 mg/L is susceptible by the available Enterobacterales criteria. Amikacin at 32 mg/L is not fully susceptible; by CLSI it is intermediate, so it must not be reported as susceptible. The laboratory should report the carbapenem results clearly, confirm the carbapenemase mechanism, and avoid issuing a misleading “pan-susceptible” or “pan-resistant” label. Tigecycline should carry a comment that it is not preferred as monotherapy for bloodstream infection because of low serum concentrations. Intrinsically resistant agents, such as ampicillin and first-generation cephalosporins, should be suppressed according to the validated panel. The final report should include the confirmed mechanism when available and should be telephoned to the treating team and infection prevention because of the infection-control implications.
2. Explain how you would use mCIM/eCIM and PCR, and why the resistance mechanism matters for therapy.
Read the worked answer
The modified carbapenem inactivation method screens for carbapenemase production. A positive mCIM indicates a carbapenemase; the eCIM, which contains EDTA, distinguishes metallo-β-lactamases from serine carbapenemases. If the mCIM is positive and the eCIM is negative, a serine carbapenemase such as KPC or OXA-48 is likely. If the eCIM is positive, a metallo-β-lactamase such as NDM, VIM, or IMP is likely. Multiplex PCR for blaKPC, blaNDM, and blaOXA-48 confirms the gene and is faster and more specific. The mechanism matters because ceftazidime-avibactam inhibits KPC and many OXA-48 enzymes but is not active against NDM or other metallo-β-lactamases. If PCR shows blaNDM, the apparent ceftazidime-avibactam susceptibility must be interpreted cautiously and the result should not be used to guide monotherapy without expert review. A KPC result supports ceftazidime-avibactam as a targeted option. The laboratory should report the mechanism and comment on its therapeutic relevance rather than leaving the clinician to infer it from the MIC alone.
3. What infection prevention and notification actions are indicated, and how should the single positive blood culture be weighed?
Read the worked answer
The patient should be placed in a single room with contact precautions, and infection prevention should be notified immediately. Staff should use gloves and gowns, perform hand hygiene, and follow the unit’s policy for carbapenem-resistant Enterobacterales, including environmental cleaning and screening of contacts if required. The laboratory should notify the treating team and infection prevention of the confirmed carbapenemase result, and should report the organism to the Kuwait Ministry of Health if it appears on the current notifiable or antimicrobial-resistance reporting list. The single positive aerobic bottle should not be dismissed as contamination: Gram-negative rods in blood are uncommon contaminants, and this patient has fever, hypotension, and intensive care risk factors. The other negative bottles may reflect prior antibiotics, intermittent bacteraemia, or low blood volume. Repeat blood cultures should be taken to assess clearance and to exclude a second organism. The laboratory should retain the isolate for confirmatory testing and outbreak investigation. The final report should combine the organism identification, susceptibility profile, resistance mechanism, and infection-control advice in a clear comment.