Detection of OXA carbapenemases and molecular mechanism in nosocomial outbreak caused by multi-drug resistant Acinetobacter baumannii strains

Objective To investigate the prevalence of OXA carbapenemases,gene homology and transmission mechanism of multidrug resistant Acinetobacter baumannii strains in this hospital,identify their characteristics of drug resistance patterns,and provide the evidence for clinical prevention and treatment.Methods Minimum inhibitory concentrations (MIC) of Acinetobacter baumannii strains were determined by agar dilution method.Carbapenemase was detected by modified Hodge test.The genotypes of OXA carbapenemase were detected by PCR and DNA sequencing.Genetic homology of Acinetobacter baumannii was analyzed by enterbacterial repetitive intergenic consensus (ERIC)-PCR and Acinetobacter baumannii gene was localized by transfer bonding technique.Results Forty-five isolates were identified as seriously drug-resistant.Among the 42 carbapenem-resistant Acinetobacter baumannii 34 were found to produce OXA carbapenemase by detection of phenotype and genotype,39 strains was positive ISAba1-blaOXA-23,3 strains was positive blaOXA-23.In all of the 42 strains blaOXA-23 was located in bacteria1 chromosomes.Among the 3 strains with positive blaOXA-58,blaOXA-58 gene of 2 strains located in bacteria1 chromosomes while the other 1 strain located in plasmid.The 42 Acinetobacter baumannii strains with blaOXA-23 belonged to 6 types (A-F) respectively.Thirty-four of them belonged to type A,four belonged to type B,and the 38 strains had genetic relationship with each other.Conclusion Production of OXA-23 carbapenemase-produced strains of Acinetobacter baumannii was the main mechanism for the multi-drug resistance for carbapenem in this study.The nosocomial outbreak was caused by clonal epidemic transmission of Acinetobacter baumannii strain carried blaOXA-23.