Carbapenemases Detection And Molecular Epidemiological Study Of Acinetobacter Baumannii

ObjectiveTo investigate the resistance and carbapenem-producing situations of clinical isolates from the First Affiliated Hospital of Anhui Medical University;To detect Genotype ofβ-lactamase and OXA type carbapenemase gene distribution of acinetobacter baumannii.so as to guide the rational use of antibiotics in clinical and reduce the difficulty of clinical treatment;To investigate carbapenem-resistant Acinetobacter baumannii status of homology,to analysis the molecular epidemiological characteristics of nosocomial resistant isolates,guidnce to controlling outbreak of resistant isolates at the hospital.Materials and methodsA total of 141 clinical isolates were collected from october 2006 to november 2008 at the First Affiliated Hospital of Anhui Medical University. Agar dilution method was used to test minimum inhibitory concentrations(MICs)of 14 antibiotics, Hodge test was used to detect carbapenemases, PCR was used to screen genotypes of beta-lactamases, OXA gene were assayed by TA-cloning and sequencing,gene location of OXA were determined by transfer bonding test. The homology of Acinetobacter baumannii isolates (carrying OXA gene) was investigated by ERIC-PCR, The genetic homology of the carbapenem-resistant isolates was determined by pulsed field gel electrophoresis(PFGE).ResultsThe resistance rates of 141 isolates to piperacillin, Ceftriaxone, ceftazidime, Cefepime and Cefoperazone/sulbactam were 93.3%,89.6%,87.3%,81.3% and 44.0% respectively, to levofloxacin and Ciprofloxacin were 88.1% and 76.1%. Then ,the resistance rates to imipenem and meropenem achieved 34.3% and 41.0%, especially.The multidrug resistance Status of A.baumannii clinical isolates was severe. Carbapenemase phenotypic testing results showed that the posive isolates were 37.β-lactamase gene screening results of 141 isolates:the number of isolates detected CTX-M-1-like, CTX-M-14-like, TEM, SHV, blaOXA-23, ISAba1-blaOXA-23,blaOXA-58 and blaOXA-66 were 2,5,79,3,3,39,3 and 85 respectively. the number of isolates detected blaOXA-23,blaOXA-58, and blaOXA-66 from 37 producing carbapenemases Ab were 31,2 and 4.sequencing results showed that blaOXA-23 and blaOXA-66 were no mutation,OXA-58 gene of 1 isolate came up mutation, the mutational site located the 14th base pairs, amino acid changed from Phe to Ser,the last two isolates no mutation .The results of transfer bonding test: OXA-23 gene locaded bacterial chromosome, OXA-58 gene of 1 isolate locaded plasmid,the last 2 located bacterial chromosome.The result of ERIC-PCR showed the 42 isolates carrying OXA-23 gene were divided into six Genotypes(A,B,C,D,E,F), there are 34 strains belonging to the same genotype, a total of 38 isolates had a genetic relationship,The last 4 isolates belong to the other 2 genotypes, the 2 genotypes also existed genetic relationship. 3 isolates carrying OXA-58 gene did not have a homologous. The 20 clinical isolates of carbapenem-resistant Acinetobacter baumannii were divided into five genotype s(including two subtypes), a total of 12 isolates belong to the same genotype.ConclusionThe multidrug resistance phenomenon of Ab. were serious,the resistance to cephalosporins and other antibiotics was highly, the resistance rate to carbapenem was increasing year by year. Producing OXA enzymes were the main resistant mechanism to carbapenem for Acinetobacter baumannii. The mainβ-lactamase gene of Acinetobacter baumannii were TEM, blaOXA-23 and blaOXA-66,ISAba1 was blaOXA-23 start sequence. Phenotype and genotype test confirmed the mainly mechanism of carbapenem-resistant Acinetobacter baumannii was producing OXA-23-type enzyme. OXA gene located bacterial chromosome.The Acinetobacter baumannii carrying OXA-23 gene exested high homology. The result of PFGE analysis showed there were high homology in Carbapenem-resistant Acinetobacter baumannii strains.so there were carbapenems-resistance isolates clone spread at the hospital.