Recommended Antibiotic Regimen for Klebsiella aerogenes Infection
For Klebsiella aerogenes infections in adults, treat with cefepime-zidebactam as first-line therapy, or alternatively use aztreonam-avibactam or ceftazidime-avibactam, based on the most recent 2025 data showing >90% susceptibility rates for these novel β-lactam/β-lactamase inhibitor combinations.
Treatment Algorithm
Step 1: Assess Resistance Profile
- Obtain susceptibility testing immediately - K. aerogenes frequently harbors AmpC β-lactamases and may co-produce ESBLs 1
- K. aerogenes shows heterogeneous resistance patterns, making empiric therapy challenging without susceptibility data 1
Step 2: First-Line Antibiotic Selection
Preferred agents (in order of susceptibility):
- Cefepime-zidebactam (97.4% susceptibility) 1
- Aztreonam-avibactam (92.7% susceptibility) 1
- Ceftazidime-avibactam (91.4% susceptibility) 1
- Meropenem-vaborbactam (91.3% susceptibility) 1
Step 3: Alternative Options Based on Resistance Mechanisms
If ESBL-producing K. aerogenes:
- Temocillin via continuous infusion (6g/day) is effective against CTX-M-15 producers and provides better sustained bacterial suppression than intermittent infusion 2
- Avoid temocillin intermittent infusion due to higher regrowth rates 2
If carbapenem-resistant non-carbapenemase-producing:
Step 4: Avoid Traditional Agents
Do not use as monotherapy:
- Gentamicin - despite historical use 3, contemporary data shows 83.74% resistance rates 4
- Amoxicillin, ampicillin, ceftazidime, tetracycline - all show 100% resistance in recent surveillance 4
- Azithromycin (89.54% resistance), cefoxitin (86.04% resistance), cefuroxime (77.90% resistance) 4
Critical Considerations
Combination Therapy for Severe Infections
For critically ill patients or those with septic shock:
- Use combination therapy with two in vitro active antibiotics 5
- This approach showed mortality benefit (OR 0.52,95% CI 0.35-0.77) in carbapenem-resistant Enterobacterales with severe disease 5
- Polymyxins and tigecycline particularly benefit from companion drugs 5
Carbapenem Use in Resistant Strains
- If carbapenem-resistant but MIC ≤8 mg/L, consider carbapenem-based combination therapy 5
- Colistin-meropenem combination showed trends toward lower mortality (21% vs 35%) though not statistically significant 5
Common Pitfalls to Avoid
- Assuming susceptibility without testing - K. aerogenes harbors blaTEM genes in 100% of recent isolates 4
- Using intermittent infusion for temocillin - continuous infusion prevents resistance emergence more effectively 2
- Monotherapy in severe infections - combination therapy reduces mortality in high-risk patients 5
- Relying on older aminoglycoside data - gentamicin resistance is now widespread despite historical recommendations 3, 6, 4
Prognostic Context
K. aerogenes BSI carries better prognosis than K. pneumoniae or E. cloacae (6.9% vs 19-20.8% mortality/recurrence), though not statistically significant 7. However, device-related infections and prolonged fever are more common with K. aerogenes 7, warranting close monitoring even with appropriate therapy.