Colistin – resistant enterobacter

1. Verify susceptibility testing

• Enterobacter spp. often carry AmpC β-lactamase → resistant to many β-lactams.
• Colistin resistance limits polymyxin use.
• You need to carefully check if the lab reported susceptibility to:
  • Carbapenems (meropenem, imipenem, ertapenem)
  • Ceftazidime–avibactam (CAZ-AVI)
  • Tigecycline

2. Potential therapeutic options

1. Carbapenems (if susceptible)
   • Meropenem is standard in neonates and infants.
   • However, many MDR Enterobacter are carbapenem-resistant.
2. Ceftazidime–avibactam
   • Active against many KPC and OXA-48 producers.
3. Tigecycline
   • Broad activity against MDR Enterobacteriaceae.
   • Concerns in neonates/infants: risk of teeth/bone effects and limited PK data. Used as salvage therapy.

3. Combination therapy

• In such resistant cases, monotherapy is risky.
• Options include:
  • Meropenem (if MIC borderline) + aminoglycoside (amikacin/gentamicin, if susceptible).
  • Ceftazidime–avibactam + aztreonam (especially if MBL [metallo-β-lactamase] suspected).