Effect of Antibiotic Combinations on the Sensitivity of CarbapenemResistant Acinetobacter baumannii Strains

Acinetobacter baumannii is one of the predominant pathogens involved in hospital acquired infections worldwide. Despite intensive surveillance and preventive measures, these infections are major cause of high mortality rates. In this study a total of 375 A. baumannii isolates were isolated from a variety of clinical collected from 5 different hospitals in Great Cairo. These isolates were identified as A. baumannii biochemically, by API20E system and genetically by detection of 16S rRNA gene. All isolates showed positive results and confirmed for the presence of the suspected gene by PCR. The antibiotic susceptibility patterns for the isolated A. baumannii were also evaluated. The detection of the presence of OXA-type (OXA 23, 24, 51 and 58) carbapenemases-encoding genes which are responsible for carbapenem resistance was also performed. I observed the presence of OXA 23 gene in 84% of the isolates. While 35.2% were positive to OXA 24 gene and 87.2% were positive to OXA 51 gene. No isolates showed positive results for the presence of OXA 51 gene. They were also evaluated for the effectiveness of drug combination of carbapenems and colistin against 30 isolates. Regarding imipenem and colistin combination, 13.3% of the strains showed synergy, while 86.7% showed additive results. For the combination of meropenem and colistin, 66.7% of the strains showed synergy, while 33.3% showed additive results. The antibacterial effect of both combinations on A. baumannii showed commonly synergistic or additive results. To a significant extent meropenem and colistin showed a superior synergy compared to imipenem and colistin.