Abstract:

Objective To investigate the gene homology of Acinetobacter baumannii clinical isolates in hospital, and explore the main carbapenems resistance mechanism of Acinetobacter baumannii. Methods The minimal inhibitory concentrations of 12 antimicrobial agents against 81 Acinetobacter baumannii clinical isolates were determined by agar dilution method. Pulsedfield gel electrophoresis (PFGE) was employed to type 81 Acinetobacter baumannii isolates. PCR was used to detect the genes of β-lactamases and main structural genes of adeABC, adeIJK and adeFGH efflux pump system, and the distributions of these genes in imipenem resistant Acinetobacter baumannii group and imipenem sensitive Acinetobacter baumannii group were compared. Results Eighty-one Acinetobacter baumannii clinical isolates were commonly resistant to 12 antimicrobial agents, with the lowest resistance rate of 30.9% for polymyxin B, the second lowest resistance rate of 53.1% for imipenem, and resistance rates over 60% for the other antimicrobial agents. Eighty-one Acinetobacter baumannii strains were classified into 7 types based on PFGE pulsotypes, named type A, B, C, D, E, F and G. Isolates of type A were the main epidemic strains. All the strains carried OXA-51 gene, and OXA-24, OXA-58, VIM-1 and VIM-2 genes were not detected. The detection rates of AmpC, OXA-23 and IMP-1 of β-lactamase genes were 83.9%（68/81）, 71.6% (51/81) and 54.3%(44/81) respectively, and those of adeB, adeJ, and adeG of efflux pump genes were 77.8% (63/81), 92.6% (75/81) and 90.1% (73/81) respectively. Statistical analysis revealed that the distribution rates of AmpC (χ²=8.9, P<0.05), OXA-23 (χ²=28.05, P<0.05), adeB (χ²=9.5, P<0.05) and adeG (χ²=5.20, P<0.05) in imipenem resistant Acinetobacter baumannii group were significantly different from those in imipenem sensitive Acinetobacter baumannii group. Conclusion There has been clonal spread of Acinetobacter baumannii stains among patients in hospital, which are mainly type A strain. β-lactamases genes Amp-C and OXA-23 and efflux pump systems adeABC and adeFGH may play an important role in the carbapenems resistance mechanism of Acinetobacter baumannii.

Key words: Acinetobacter baumannii, pulsed-field gel electrophoresis, resistance mechanisms