[Combined drug sensitivity test of 50 strains of extensively drug-resistant Acinetobacter baumannii]

Abstract

Objective: To study the in vitro antibacterial activity of meropenem combined with doxycycline, ciprofloxacin, sulbactam or cefoperazone/sulbactam against clinically isolated extensively drug-resistant Acinetobacter baumannii (XDRAB).

Methods: Using a checker board synergy design, the minimal inhibitory concentration (MIC) of antibiotics against 50 isolates of XDRAB was determined by broth microdilution antifungal susceptibility test. The fractional inhibitory concentration (FIC) index was calculated to determine the combined effect of the antibiotics.

Results: Meropenem showed significantly reduced MIC50 and enhanced antimicrobial activities when combined with doxycycline, sulbactam or cefoperazone/sulbactam. The FIC results suggested that the main actions of doxycycline, sulbactam, and cefoperazone/sulbactam were synergistic (38%, 26%, and 10%, respectively) and addictive (62%, 74%, and 90%, respectively) without indifferent or antagonistic effects. The main actions of meropenem combined with ciprofloxacin were additive (56%) and indifference (44%) with synergistic and antagonistic effects.

Conclusion: Meropenem combined with doxycycline, sulbactam or cefoperazone/sulbactam shows excellent activity against clinical isolates of XDRAB.