Role of efflux pumps in resistance to tigecycline in Acinetobacter baumannii

Abstract

To investigate the role of active efflux pumps in mediating the resistance of Acinetobacter baumannii to tigecycline. The in vitro susceptibility of Acinetobacter baumannii to tigecycline was determined by broth microdilution method. Minimal inhibitory concentrations (MICs) of tigecycline against Acinetobacter baumannii strains were determined by broth microdilution method with or without efflux pump inhibitors of Carbonylcyanide-m-chlorophenylhydrazone (CCCP). Efflux pumps genes including adeB, adeJ and abeM were amplified by polymerase chain reaction (PCR) and sequenced. The expression levels of these genes were measured using quantitative real-time transcription- polymerase chain reaction (RT-PCR). The modulating gene adeR and adeS were detected by PCR amplification, deoxyribonucleic acid (DNA) sequencing were performed with specific primers and were compared with the published sequence online. The sensitive rate of Acinetobacter baumannii to tigecycline was 22.39% (15/67), active efflux of drugs existed. The adeB gene was positive in 88.06% (59/67) out of 67 Acinetobacter baumannii strains, and adeJ and abeM were 100% positive. adeB and adeJ genes expression in clinical isolates of resistant Acinetobacter baumannii increased 17.88-fold and 6.07-fold than sensitive strains, respectively. AbeM gene expression in resistant strains had not significant increase. The sequence of adeR and adeS genes in clinical isolates of sensitive and resistant strains were the same except several point mutations. Efflux pump systems of AdeABC and AdeIJK may play a role in Acinetobacter baumannii resistant to tigecycline in western China, AbeM may be irrelevant to it. The point mutations of adeR and adeS may not up-regulate the transcription activities of adeB in this study.