Investigation of the synergistic effects of various antibiotic combinations in acinetobacter baumannii isolates using the checkerboard method

Acinetobacter genus bacteria are considered as one of the most often isolated agents during the recent years especially in the intensive care units as nosocomial infections. In the last years, this microorganism is seen as a pathogen with multiple drug resistance which is seen in pneumonitis, urinary tract infections, septicaemia and menengitis. Nowadays, the resistance against antimicrobial agents used for treatment of infections caused by Acinetobacter baumannii strains have also become an important medical problem in our country. The fact of Acinetobacter baumannii becoming a more common infection agent and the increase upon the antimicrobial resistance has required researches upon new drugs. This study was done at Microbiology Laboratory of Abant Izzet Baysal University Faculty of Medicine. A total of 30 Acinetobacter baumannii strains isolated from various clinical samples during 01/04/2009-20/11/2013 were included in the study. The identification of the bacteria was done in species level using BD Phoenix 100 system (Becton Dickinson, Sparks, Maryland, USA).The antibiotic susceptibilities of A. baumannii strains were identified using the disc diffusion method. Antibiotic susceptibility breakpoints were evaluated according to the Clinical and Laboratory Standards Institute 2014 criteria. Colistin-vancomycin, colistin-imipenem, colistin-sulbactam, imipenem-sulbactam combination efficiencies of 12 Acinetobacter baumannii strains which have shown multiple drug resistance were examined with checkerboard method. Results of the four combinations with checkerboard method has shown that colistin-sulbactam combination had additive effect in nine isolates (%75), and was non-effective in three isolates (%25); colistin-vancomycin combination had additive effect in seven isolates (%58,3), and promiscous effect in five isolates (%41,7); imipenem-sulbactam combination had promiscous effect effectin 12 isolates (%100) according to the fractional inhibitory concentration index rates. In conclusion, our studys howed that Acinetobacter baumanii isolates with multiple drug resistance had mostly high Minimum Inhibitory Concentration (MIC) rates. No synergic or antagonist effects were found. For prevention of the increase in the resistance rates, antibiotic combinations with appropriate indications should be used, and the efficiency of the antimicrobial agent combinations determined as effective with in vitro studies on Acinetobacter baumannii strains should be examined with further clinical trials. Keywords: Acinetobacter baumannii, synergistic effect, checkerboard, colistin, vancomycin, imipenem, sulbactam.