AdeABC efflux pump: Less important role in Acinetobacter baumannii against carbapenems

Abstract

AdeABC efflux pump in a total of 50 Acinetobacter baumannii strains were investigated and the role in contributing to hydrolysis carbapenems were further analyzed. All strains were divided into 3 groups according to their susceptibilities to Imipenem, Amikacin, Minocycline and Levofloxacin: Group A (22 imipenem-resistant strains), B (13 isolates which were imipenem-sensitive but resistant to at least one of the other three antibiotics) and C (15 isolates, sensitive to all the antimicrobials). Five gene types were observed according to REP-PCR and 39 isolates were included in the main one. Only one isolate (A2) was positive for efflux pump phenotype. All strains were positive for blaOXA51-like and AdeB gene and negative for blaOXA24, blaOXA58, VIM, IPM, and SIM-1. blaOXA23 were detectable merely in the 22 imipenem-resistant strains. 24 isolates from the same REP type representing for the 3 groups were selected for quantitative analysis of adeB expression. Compared with the mean level of Group B, only A2 expressed apparently higher (2.2 fold). The induction effects of imipenem and meropenem were analyzed as well. Compared with their freely grew isogenic counterparts, up regulated expression was observed only in 2 isolates under the pressure of imipenem and none in all under meropenem. These data indicate that AdeABC efflux pump play a less important role in A. baumannii against carbapenems. Key words: Acinetobacter baumannii, Carbapenem resistance, AdeABC efflux pump, adeB gene.