Objective: To survey antibiotic resistance of clinical isolates of Acinetobacter baumannii in Changsha and to investigate molecular epidemiological characteristics of carbapenem-resistant Acinetobacter baumannii.
Methods: A total of 205 non-duplicated, clinical isolates of Acinetabacter baumannii from 10 general hospitals in Changsha were collected from March 2010 to December 2010. The K-B disk diffusion method was applied for the drug-susceptibility test; a modified, double-disk synergy test was used to detect metallo-β-lactamase (MBL), and a modified Hodge test was used for the screening of carbapenemase. PCR was used to amplify carbapenemase genes (including OXA-23, OXA-24, OXA-51, IMP-1, and VIM-2) and the positive products were sequenced. Enterobacterial repetitive intergenic consensus PCR (ERIC-PCR) was used for DNA typing and test of homology.
Results: Of the 18 antibiotics tested, 14 had a high rate of resistance (>50% of the isolates tested), with piperacillin the highest (80.5% of strains), and cefoperazone/sulbactam the lowest (2.5%). In total, 115 carbapenem-resistant Acinetobacter baumannii strains were confirmed, but their MBL phenotype and genes were all negative. Seventy-one positive strains were detected by the modified Hodge test, among which 64 strains were OXA-23-positive. All the 115 strains were positive for the amplification of the OXA-51 gene, and no strain was found which carried OXA-24 or OXA-58 gene. Seven genomic types were included in the 115 Acinetobacter baumannii. The major prevalence types were Type B ( 72 strains) and Type A (19 strains).
Conclusion: Multiple drug resistance of clinically isolated Acinetobacter baumannii is a serious problem in Changsha. Production of OXA-23 and OXA-51 carbapenemases is an important mechanism of resistance to carbapenem antibiotics, and there is prevalence of the same clones in these carbapenem-resistant strains.