Abstract

COLISTIN EXHIBITS DIVERSE AND STRAIN DEPENDANT SYNERGY IN COMBINATION WITH DIFFERENT ANTIBIOTICS AGAINST ACINETOBACTER BAUMANNII STRAINS

Khine Swe Swe Han*, Kamaludeen Baba, Koleka P. Mlisana, Manormoney Pillay

ABSTRACT

Drug resistant Acinetobacter baumannii is a serious problem in clinical settings worldwide and has a significant effect on the optimal use of antibiotics, especially in patients with polymicrobial infections. This study was conducted to determine the effectiveness of various antibiotic with colistin combinations against A.baumannii using synergy testing. A.baumannii strains were analysed for antibiotic susceptibility and synergistic efficacy of colistin in combination with carbapenems, amikacin, piperacillin-tazobactam, ciprofloxacin, vancomycin, linezolid and rifampicin. In vitro synergy tests were performed using a colistin-incorporated plate with the Epsilometer test strip method. Of the sixty strains tested, 90% were susceptible to colistin and amikacin, 25% to carbapenems and ciprofloxacin and 20% to piperacillin-tazobactam. Although the combination of colistin and rifampicin showed synergistic effects against 28% of tested strains, while colistin combinations with carbapenems, piperacillin-tazobactam, ciprofloxacin and vancomycin each showed synergistic effects in 2-3% of tested strains. Seventeen strains (28%) showed antagonistic effects against colistin in combination with rifampicin. Synergy testing of colistin combinations yielded highly diverse and strain dependant results. Our findings suggest that synergy testing should be performed for individualised direct therapy. Optimal treatment and the role of combination therapy should be addressed in future research.

Keywords: Drug resistant Acinetobacter baumannii; polymicrobial infections; combination therapy; synergy test; individualised direct therapy; strain dependant.