The Molecular Characterization About Carbapenem-resistant Acinetobacter Baumannii

Object:To investigated the main mechanism of carbapenem-resistant Acinetobacter baumannii from clinical isolates,and their epidemical characteristics in PLA general hospital.Method:Whonet software were used to screen the carbapenem-resistant isolates of Acinetobacter baumannii(CRAB) from the lab database.Multiple PCR was conducted to detect the carbapenemase gene(including metallo-β-lactamases and oxacillinase),integron gene and insertion sequence gene of all isolates.DNA sequencing was adopted to analyze the resistance-related OXA-23 gene.The CRAB isolates from the surgery intensive care unit(SICU) were picked up from the database,the MICs of these strains were measured by using agar dilution method,the genotypes were checked using pulse-field gel electrophoresis(PFGE), and learning about the epidemical characteristics of CRAB from the SICU were studied by analyzing the result of MICs,genotypes and case histories of patients. The crystal violet stain was used to detect the formation percentage of bacterial biofilm of the CRAB from SICU,and the morphology of biofilm was watched through scanning electron microscope.Result:197 CRAB isolates were screened by Whonet software from January 2007 to December 2007.The PCR result showed that 184 strains of 197 CRAB isolates had bla_OXA-23-like,1 strain had bla_OXA-58-like,1 strain had bla_IMP,184 strains had typeⅠintegron,195 strains had IS_Aba-1,no bla_OXA-24-like,bla_VIM,bla_SIM-1 and typeⅡintegron were detected.DNA sequencings showed these 3 random selected strain which bla_OXA-23-like is positive were more than 98%homology to the EU977574.1.Among 197 CRAB isolates,40 strains were isolated from SICU's patients,another 10 strains were isolated from the SICU's environment and medical staff.All 50 strains had highly drug-resistant percentage to 10 kinds of antibiotics,only susceptible to polymycin.They could be divided into 4 genotypes, named A,B,C and D.The genotype A accounted for the most,which was the main epidemic clone.These 4 genotypes had some relationship.17 strains of the 50 CRAB from SICU could form biofilm in vitro,9 of which were isolated from environment and medical staff.Conclusion:the main carbapenem-resistant genes of CRAB in 2007 were bla_OXA-23-like and bla_OXA-51-like,which produced the OXA-23 class and OXA-51 class carbapenemases.The molecular epidemiological research about SICU's CRAB showed that most strains belonged to genotype A,including the strains from environment and medical staff.It indicated the trend of CRAB strains from SICU transmission with single clone.The bacterial biofilm could protect CRAB from the risk of environment,and prolong the surviving period of CRAB,which maybe involved pathogenesis of the CRAB.