In vitro postantibiotic effect of colistin on multidrug-resistant Acinetobacter baumannii

Infections by multidrug-resistant Acinetobacter baumannii constitute an increasing threat for critically ill patients. Colistin is often the only antimicrobial retaining activity against these strains. The postantibiotic effect (PAE) of colistin was studied on 19 isolates of A. baumannii resistant to ampicillin/sulbactam, ciprofloxacin, and carbapenems with the viable count method. The mean PAEs of 1x MIC and 4x MIC concentrations of colistin on the tested isolates were 3.90 and 4.48 h, respectively, indicating that a modified dosage scheme with increased dosing intervals might retain activity whereas minimizing the incidence of adverse effects.