Characterization and distribution of drug resistance associated β-lactamase, membrane porin and efflux pump genes in MDR A. baumannii isolated from Zhenjiang, China

Acinetobacter baumannii (A. baumannii), especially the multidrug resistant A. baumannii (MDR-AB) is becoming a common opportunistic pathogen in hospital, and constitutes significant public health threats. This study aimed at investigating the relationship between drug resistance with expression of class A-D β-lactamase genes, mutation in membrane porin and over-expression of efflux pump genes among A. baumannii isolated from Zhengjiang, China. Antibiotic susceptibility assays were performed using Kirby-Bauer disc diffusion method. PCR was used to detect β-lactamase genes and carO, oprD, adeR, adeS. Real-time PCR was used to assess the mRNA expression level of efflux pump gene adeB. The software of DNAMAN was applied to assemble oprD and carO sequences, and the sequences were compared with those retrieved from GenBank (http://www.ncbi.nlm.nih.gov/). 27 isolates (61.4%) in this study were MDR-AB, in which five β-lactamases including TEM, CTX-M-2, ADC, OXA-23 and OXA-51 were found, and the positive rate was 96.3% (26), 14.8% (4), 92.6% (25), 88.9% (24) and 92.6% (25), respectively. In addition, the expression level of adeB mRNA was significantly increased in MDR-AB, it might due to adeR mutation. Some mutations were also found in carO and oprD. MDR-AB showed high relationship with β-lactamase, mutation in membrane porin and overexpression of adeB, which may directly relates to the mutation in regulating gene adeR.