Resistance and heteroresistance to colistin among clinical isolates of Acinetobacter baumannii

Colistin is one of the most effective alternatives for treating Acinetobacter baumannii infections. The aim of this study was to determine colistin resistance and heteroresistance rates in A. baumannii from clinical samples in Hacettepe University clinical microbiology laboratory between June 2016 and January 2017. A total of 200 isolates were included in the study. In vitro susceptibility to amikacin, gentamicin, ceftazidime, piperacillin/tazobactam, meropenem, ciprofloxacin, and tigecycline were determined by disk diffusion test. Most isolates were multiresistant as they exhibited resistance to aminoglycosides, beta-lactams, and fluoroquinolones. Colistin susceptibility was determined by broth microdilution (BMD) test (EUCAST standards) and was compared with E-test (bioMerieux, France) in 120 isolates. In 14 blood isolates that were susceptible to colistin (MIC