| Objective: To investigate the drug resistance (antimicrobial sensitivity patterns and genetic mechanisms) of clinical isolated Acinetobacter baumannii (AB) to20kinds of clinical commonly used antimicrobial agents in northeast Sichuan areas for guide the clinical effectively controlled infection and transmission of drug-resistant strains in the hospital.Methods: MICs of20kinds of antimicrobial drugs against clinical isolates of ABs were measured using the agar dilution method and the same approach was used to measured MICs of4antimicrobial drugs after using efflux pump inhibitors; PCR was performed for detecting the distribution of the efflux pumps genes (adeB, adeJ, abeM), the class D carbapenemase-encoding gene and insert sequence ISAba1(OXA-23, OXA-24, OXA-51, OXA-58and ISAba1), and outer membrane protein-encoding gene carO; the RT-PCR technique was used to detect the expression of efflux pump genes (adeB, adeJ, abeM) and the ISAba1downstream gene(OXA-23, OXA-51). SDS-PAGE was used to analyze the expression of outer membrane protein.Results:110strains of Acinetobacter baumannii to polymyxin B showed the highest sensitivity (100%) and the resistance rate of Imipenem and Meropenem were28.18%and29.09%, the resistance rate for the other17kinds of drugs were between50.00%and99.09%. The Multidrug-resistance rate of carbapenem-resistant Acinetobacter baumannii was100%and the Extensively Drug Resistance rate was56.25%. Efflux pump inhibition test showed that the positive rate of gentamicin+CCCP was the highest (74.55%; 82/110).15efflux positive strains were selected by Meropenem+CCCP, which accounting for28.13%in Meropenem-resistant strains. The detection rate of adeB, adeJ, abeM genes was78.2%,79.5%,80.8%in carbapenem-susceptible strains, respectively. However, in carbapenem-resistant strains,96.9%detected adeB, adeJ and OXA-23genes,93.8%detected abeM and100%strains carry OXA-51and carO, while all the strains were not detected OXA-24, OXA-58genes. RT-PCR results showed that the relative expression level of adeB gene in carbapenem-resistant group (group R) was0.9062±0.1732, which is significantly higher than that of carbapenem-susceptible group (group S)(0.4856±0.1576)(p<0.05). The expression of OXA-23and OXA-51genes of insert sequence ISAba1downstream increased in group R. SDS-PAGE analysis revealed that there were differential protein bands between the carbapenem-resistant strains and the sensitive strains, in which three proteins of50and22kDa were recognized as outer membrane proteins.Conclusion:1. Drug resistance of Acinetobacter baumannii clinical isolates to commonly used antimicrobial agents was serious; especially the carbapenem-resistant strains were multidrug-resistant, even pandrug-resistant.2. The high detection rate and high expression levels of efflux pumpgene adeB were related with multidrug-resistant of Acinetobacter baumannii, and AdeABC active efflux system was significant in mediating Acinetobacter baumannii resistant to Meropenem.3. OXA-23and OXA-51type carbapenemases were related withcarbapenem-resistant of Acinetobacter baumannii, and insert sequence ISAba1could influence expression of OXA-23, OXA-51gene. 4. Compared carbapenem-resistant Acinetobacter baumannii with carbapenem-susceptible strains, the changes in outer membrane protein play a certain role in the carbapenem resistance. |
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