Study On β-lactamase Genes And Integron And Phylogenetic Analysis In Multidrug-resistance Acinetobacter Baumannii(MDR-ABa)

Objective:To learn the resistance character and resistance model of multidrug-resistance Acinetobacter baumannii clinical isolates in Tianjin; to analyse the production of β-lactamases and distribution of integron and resistance gene in multidrug-resistance Acinetobacter baumannii; to study OXA-23mRNA expression associated with insertion sequence IS Abal in eight imipenem-resisrance strains; molecular epidemiology analysis was performanced to all multidrug-resistance strains.Methods:Seventy-eight isolates were collected from six hospitals in Tianjin from February in2007to February in2008, multidrug-resistance strains were picked out by Kirby-Bauer (K-B) test and microdilution test. Three-dimensional extract test was used for identification of ESBLs,AmpC-β-lactamases, metallo-lactamases (MBLs)was identified by imipenem/imipenem-EDTA combined-disk test, resistance genes and integrase gene were amplified by PCR. OXA-23mRNA expression of eight imipenem-resisrance strains was detected by real-time PCR and ISAbal was amplified by PCR. Gene cassette structure of variable region was analysed by restrict fragment length polymorphism(RFLP). Some PCR positive products were sequenced and analyzed for homology on genbank. Relationship of clinical isolates were analysed by multigene cluster typing.Results:Fifty-five multidrug-resistance Acinetobacter baumannii were picked out from seventy-eight isolates, they showed twenty-two resistance model, nine of which was common. Three-dimensional extract test demonstrated seven strains were ESBLs positive, thirty-nine strains were AmpC-β-lactamases positive, among which four strains showed ESBLs positive, imipenem/imipenem-EDTA combined-disk test showed four strains were MBLs positive. Twelve TEM type genes, five PER genes, one VEB-1gene, two IMP-1gene, three IMP-2genes, ten OXA-23genes were founded by PCR, SHV、CTX-M-I group、VIM-2、OXA-24group were negative. Real-time PCR reflected that OXA-23mRNA expression was higher in three imipenem-resisrance strains, but lower in other five strains, ISAbal was founded in all imipenem-resisrance strains. Among fifty-five multidrug-resistance Acinetobacter baumannii, forty-seven strains were I class integrase gene positive, twenty-three of which contained variable region, RFLP showed the same size variable region possess the same DNA sequence, Ⅱ and Ⅲ class integrase gene were negative. Three clone strains were founded in fifty-five multidrug-resistance Acinetobacter baumannii by multigene cluster typing.Conclusions:Fifty-five multidrug-resistance Acinetobacter baumannii showed the highest antimicrobial susceptibility to imipenem susceptibility rate was85.5%; AmpC-β-lactamases was the main β-lactamases which multidrug-resistance Acinetobacter baumannii produced; I class integrase gene was existed extensively in multidrug-resistance Acinetobacter baumannii;base mutation of IS Aba1may be to some extent influence OXA-23mRNA expression; multidrug-resistance Acinetobacter baumannii appear cross-infection among different hospitals.