Background: Acinetobacter baumannii (A. baumannii) has emerged as a nosocomial pathogen especially in the intensive care units (ICUS). It's enlisted at the top of urgent threat level organisms in CDC's antibiotic resistance threats report. Objectives: To assess prevalence, risk factors of health care associated infection by A. baumannii, and to compare the in-vitro efficacy of colistin sulfate- tigecycline combinations versus their individual combination with levofloxacin and meropenem against carbapenem resistant A. baumannii clinical isolates from an Egyptian tertiary care hospital ICUs. Methodology: The study included 250 ICU patients, samples were collected according to the site of infection. A. baumannii was isolated, identified and tested for antibiotic susceptibility by disc diffusion. Broth microdilution method was used for assessment of colistin, Tigecycline, levofloxacin, and meropenem. Thirty isolates resistant to all carbapenems were tested by the checkerboard method to assess effect of antibiotic combinations.
Results: forty-six A. baumannii were isolated, with highest prevalence in respiratory secretions. Prior antibiotic administration and failure of empirical antibiotic therapy were found to be a major risk factors of infections by A. baumannii. Colistin combination with meropenem showed the highest synergy (50%). Tigecycline-meropenem combination had the highest antagonistic effect (66.7%).
Conclusion: No antagonistic effect of colistin combination with meropenem was confirmed in this study. Only colistin-based combinations, particularly those with meropenem may confer therapeutic benefits against carbapenem-resistant A. baumannii.