Investigation of some carbapenemases by genotypic methods in multi-drug resistant Acinetobacter baumannii strains isolated from clinical specimens

In the last decades, mutiple drug resistance, including carbapenems, made it difficult to treat infections due to Acinetobacter baumannii. We aimed to determine the antimicrobial susceptibility of A. baumannii and investigate the presence of OXA type beta lactamase genes admitted as the most important reasons of carbapenem resistance in A. baumannii. Eighty A. baumannii strains isolated from intensive care units of Dicle University Hospitals between December 2012 and February 2013 were identified with conventional methods and automated microbiology system BD Phoenix (Becton Dickinson, USA). The antibiotics susceptibility tests of the isolates were performed with both automated system and disc diffusion method. The hyplex® CarbOxa ID test system was used for amplification of blaOXA-51-like, blaOXA-23-like ,blaOXA-58-like and blaOXA-40-like gene clusters by multiplex PCR and hybridisation of the polimerase chain reaction (PCR) products to specific oligonucleotide probes in an enzyme-linked immunosorbent assay (ELISA)-based system. All isolates (100%) were found to be susceptible to colistin while the susceptibility rates of tygecycline, netilmicin, amikacin, trimethoprim-sulfamethoxazole, gentamicin and cefoperazone-sulbactam were 27.5%, 22.5%, 16.25%, 12.5%, 8.75% and 5% respectively. Two strains showed intermediate susceptibility for levofloxacin while all of the isolates were resistant against any remaining tested antibiotics (ampicillin-sulbactam, piperacillin-tazobactam, ceftazidime, cefepime, cefotaxime, ceftriaxone, imipenem, meropenem, ciprofloxacin). Among 80 isolates, 77 (%96.25) of them were positive for blaOXA-51-like genes which were consistantly found and unique to A. baumannii. BlaOXA-23-like, blaOXA-58-like and blaOXA-40-like genes were demonstrated in 48 (%60), 12 (%15) and 8 (%10) isolates respectively. Fortyseven isolates (%58.75) were positive for both blaOXA-51-like and blaOXA-23-like genes, while 10 (%12.5) isolates for both blaOXA-51-like and blaOXA-58-like genes.