Study On The Mechanism Of Active Eflfux-medicated Multidrug Resistance In Acinetobacter Baumannii Isolates

Objective: To survey the drug resistance of Acinetobacter baumannii inclinical isolates to20commonly used antimicrobial agents, analyze thedistribution and characterization of three RND efflux systems, the disinfectantresistant gene of qacE△1and the tetracycline resistance genes in order toprovide important experimental data for control of multidrug resistantAcinetobacter baumannii infections.Methods: The minimum inhibition concentrations (MICs) of20Antimicrobial drugs against to clinical isolates of112Acinetobacterbaumannii (from the Affiliated Hospital of North Sichuan Medical College)were determined with agar dilution on the basis of CLSI. The influence ofactive efflux inhibitors CCCP on the strain of MIC was detected by using theagar dilution method. The chromosomal DNA was amplified by PCR usingprimers of the RND efflux pump genes (adeB, adeJ, adeG), the disinfectantresistant gene of qacE△1and the tetracycline resistance genes (tetA, tetB),and the relationship between the genetic detection rates and the multiple drugresistance was analyzed.Results:112isolates of A. baumannii were isolated mainly from the ICU(38.4%) and the Department of Respiratory Diseases (16.1%). The mainsource of specimens was sputum (75.0%). Of the112Acinetobacterbaumannii isolates, the sensitive rates of Polymyxin B, Imipenem andMeropenem were100%,82.4%and86.8%, respectively. The rest of thesensitive rates were lower, between4.3and53.9%. The resistance rates of commonly used cephalosporins (except cefepime), penicillin, aminoglycosideand quinolones were more than70%. Study of susceptibility showed that87strains (75%),18strains (16.1%),13strains (11.6%),2strains (1.7%) showedpositive efflux when gentamicin chloramphenicol, tetracycline and cefazolinwere used together with CCCP, respectively. When the112isolates of A.baumannii were treated with CCCP, the MICs of gentamicin showed asignificant decrease.The positive detection rates of adeB、adeJ and adeGreached64.3%(72/112),75.9%(85/112) and57.1%(64/112), respectively.49.1%of the isolates, which contained adeB, adeJ and adeG, had the highestdrug resistance to five kinds of drugs, including ceftriaxone, cefepime,gentamicin, tetracycline and chloramphenicol. The isolates with all adeB,adeJ and adeG had levels of resistance, to seven kinds of drugs, significantlyhigher than the isolates with only adeB, with only adeJ or without adeB, adeJor adeG.The disinfectant resistant gene of qacE△1was detected in73.2%(82/112) of the isolates. For most antibacterials tested, the resistant rates ofidisinfectant resistant gene strains were higher than those of disinfectantresistant gene negative strains. The incidence (90.2%) of multidrug resistantisolates in disinfectant resistant gene positive strains was much higher thanthat (70.0%) in disinfectant resistant gene negative strains. Of the112Acinetobacter baumannii isolates,(i)76were resistant to tetracycline, ofwhich32.8%(25/76) were positive with tetA,73.6%positive with tetB and30.2%with both tetA and tetB;(ii)29were sensitive to tetracycline, of which3.4%(1/29) were positive with tetA,6.9%positive with tetB;55.3%werepositive with tetB, The incidence (96.7%) of multidrug resistant isolates intetB gene positive strains was much higher than that (70.0%) in tetB genegene negative strains. Conclusions：1.Acinetobacter Baumannii isolated from local areas were extensivelyresistant to most commonly used antimicrobial agents; Polymyxin B,minocycline, imipenem and meropenem are the most effective agents againstinfections of multidrug resistant A. Baumannii.2.Higher coexistence of adeB with adeJ and adeG RND efflux pumpstructure of genes was found in A.baumannii clinical isolates, which wascorrelated with multiple drug resistance.3.High incidence of qacE△1was found in A. baumannii clinical isolates,which played an important role in multidrug resistance of Acinetobacterbaumannii.4.The tetA and tetB genes were found in tetracycline-resistantA.baumannii isolates, and in particular, the tetB detection rate was higher,which was closely correlated with tetracycline antibiotic resistance.