Synergistic combination of colistin with imipenem,amikacine or ciprofloxacin against Acinetobacter baumannii and Pseudomonas aeruginosa carbapenem-resistant isolated in Annaba hospital Algeria

Objective: The aim of this study is to detect in vitro the synergetic activity of colistin in combination withimipenem, amikacin or ciprofloxacin, at sub-inhibitory concentrations, against carbapenems-resistant (CR) Acinetobacterbaumannii and Pseudomonas aeruginosa strains isolated from various wards in Annaba teaching hospital in eastern Algeria.
Materials and Methods: The minimal inhibitory concentrations (MIC) were determined by broth macrodilution (BMD).Carbapenemase encoding genes were screened using polymerase chain reaction (PCR). The activity of colistin incombination with second antibiotic was evaluated by the Checkerboard Technique.
Results: 39 CR P. aeruginosa and 21 CR A. baumanni strains where collected. The MIC values ranging from (0.25 to4 µg/ml) to colistin, ≥16 µg/ml for imipenem, ≥4 µg/ml to amikacin and ≥8 µg/ml ciprofloxacin. The PCR reveals thepresence of the genes bla_OXA23 (n = 12), blaOXA24 (n = 6), blaNDM1 (n = 3) in A. baumannii and blaVIM2 (n = 12) in P.aeruginosa. The combination of colistin with imipenem showed synergistic effect on 57.14% and 46.15% of A.baumannii and P. aeruginosa isolates, respectively. For colistin and amikacin, the synergistic effect is detected in 28.6%of A. baumannii and 30.8% of P. aeruginosa. While colistin and ciprofloxacin showed synergy on 14.29% and 15.38% ofA. baumannii and P. aeruginosa isolates, respectively.
Conclusion: CR A. baumannii and P. aeruginosa remain the most prevalent infection agents in patients from high-riskwards at Annaba Hospital. Colistin associated with imipenem or with amikacin at sub-inhibitory concentrations givesvery encouraging results allowing better management of infections caused by this type of bacteria.