Functional analysis of multidrug efflux pumps genes of Acinetobacter baumannii strains

Efflux systems are components of the bacterial membrane that play a role in homeostasis of the cell and extrusion of toxic compounds. Efflux pumps of the resistance nodulation cell division (RND) superfamily، confer multidrug resistance to their host when over-expressed. One of the RND efflux systems، is AdeABC which have been characterized for A. baumannii. Another pump belonging to the MATE family، AbeM، has been characterized. The aim of this study was to analysis the expression and function of multidrug efflux pumps of Acinetobacter baumannii strains. The descriptive study was done during a period of 18 month. A total of 194 isolates of A. baumannii were studied using Rep-PCR، disk diffusion test، and E-test. Gene expression and function of efflux pumps were evaluated in 50 non-clonal multidrug resistant clinical isolates of A. baumannii via real-time PCR and ethidium bromide accumulation. The resistance rates against the tested antibiotics ranged from 69 to 99% with all isolates harboring adeB (100%) and abeM (100%) genes. No mutation was detected in adeS or adeR gene. An expression of adeB mRNA is correlated with reduced susceptibility to Cefepime but not other antibiotics. The expression of abeM was not associated with changes in MICs. It seems that several mechanisms are involved in multidrug resistance of A. baumannii. The increased expression of adeABC is not the main contributor for antibiotic resistance.