Antimicrobial Susceptibilities of Clinical Acinetobacter baumannii Isolates With Different Genotypes

The treatment of Acinetobacter baumannii infections is difficult. Carbapenems, sulbactam, and colistin are the most effective antibiotics.

The aim of this study was to evaluate the susceptibilities of genotypically different A. baumannii isolates to sulbactam, amikacin, netilmicin, meropenem, tigecycline and colistin.

Isolates from various clinical samples of patients with hospital-acquired infections that were identified by the VITEK 2 Compact system in our hospital's microbiology laboratory between January 2010 and March 2012 were included in the study. To determine genetic relatedness of the isolates, the rep-PCR method was used. The broth microdilution method was used for amikacin, netilmicin, meropenem and colistin, while E-test was used for sulbactam and tigecycline.

Among the 300 isolates, 30 were found to be genotypically different and were evaluated in terms of their antimicrobial susceptibilities. All isolates were susceptible to colistin. The susceptibility rates were 66.6%, 50%, 36.6%, 30%, and 10% for netilmicin, tigecycline, sulbactam, amikacin, and meropenem, respectively. For carbapenem resistant isolates, the susceptibility rates were 66.6%, 51.8%, 33.3%, and 25.9% for netilmicin, tigecycline, sulbactam, and amikacin, respectively. The sulbactam minimum inhibitory concentration (MIC) 50 and MIC 90 were 8 μg/mL and 12 μg/mL, respectively.

In this study, it was concluded that determining the cut-off value for MIC breakpoints for sulbactam alone has a critical impact on the susceptibility results.