Study On The Control And Genotyping Of OXAase Gene In Carbapenem-resistant Acinetobacter Baumannii

ObjectiveTest the sensitivity of Acinetobacter baumannii toβ-lactam antibiotics and analyze the reasons for their drug resistance. Establish a rapid and simple method for detection ofβ-lactamase genes and analyze the association ofβ-lactamase genes with multi-drug resistance in Acinetobacter baumannii clinical isolates. Investigate the existence and expression of the OXAase gene, and explore the relationship between the exitense of regulating gene and the expression of OXAase gene in carbapenem-resistant Acinetobacter baumannii.MethodsA total of 90 non-duplicate clinical isolates of Acinetobacter baumannii were recovered and antimicrobial susceptibility was determined by disk diffusion and agar dilution.β-lactamase genes in the Acinetobacter baumannii isolates were detected using multi-PCR.The antimicrobial resistance related genes including OXAase genes(OXA-23, OXA-24, OXA-51,OXA-58), intⅠ, ISAba1 and ISAba4 genes in the carbapenem antibiotics resistant strains were detected by regular PCR. ResultsThe resistant rates of 90 strains of Acinetobacter baumannii were 83.3-94.4% to cefazolin, aztreonam, cephalothin, cefoxitin, chlorine cloxacillin, ampicillin and cefoperazone. The multiple PCR results revealed that 64.4% Acinetobacter baumannii isolated contained one to four kinds ofβ-lactamase gene, including genes for PER-1(50%), AmpC(45.8%), TEM-1 (35.1%), SHV-5 (22.4%), and CTX-M2 (6.8%). For most antibacterials tested, the resistant rates ofβ-lactamase gene-positive strains were higher than the negative strains. The incidence of multidrug resistant isolates inβ-lactamase gene-positive strains was much higher than those of negative strains. Of the 10 clinical isolates of carbapenemase positive Acinetobacter baumannii, 8 isolates were shown positive to OXA-23, 4 isolates were positive to OXA-51. 1 strain was positive to intⅠgene. The blaOXA-23 gene was found to coexist with ISAba1 gene in the 8 isolates.Conclusion1. The clinical isolates of Acinetobacter baumannii in Northeastern Sichuan were extensively resistant to most commonly usedβ-lactam antimicrobial agents.2. High incidence ofβ-lactamase genes was found in Acinetobacter baumannii isolates and close association existed betweenβ-lactamase genes and multiple drug resistance. 3. The multiple PCR system can simultaneously amplify different types ofβ-lactamase genes, which provides a method for rapid detecting of resistance genes in Acinetobacter baumannii.4. OXAase is one of the major reasons for the resistance to the carbapenem antibiotics in Acinetobacter baumannii. ISAba1 existence and OXAase gene expression are closely linked, which suggests that ISAba1 is providing the promoter for OXA-23ase gene.