The Research On Resistance Mechanism Of Acinetobacter Baumannii To Carbapenems

ObjectiveAcinetobacter baumannii(AB)is one of the main opportunistic pathogens causing nosocomial infections and has a strong dissemination ability and severe drug resistance problems.Carbapenem antibiotics are currently the last line of defense against infection by AB,while reports of drug resistance of AB are increasing.The objective of this study is to monitor the resistance of AB to carbapenems in Shenyang area,investigate the carrying situation of carbapenemase,class I integron and Tn2009 and the effect of these three genes on the drug resistance in carbapenem-resistant Acinetobacter baumannii through drug susceptibility test,phenotypic detection methods of carbapenemase and molecular biology techniques,so as to provide theoretical basis for guiding clinical rational drug use and controlling nosocomial infection.Methods45 strains of Acinetobacter baumannii were isolated from clinical specimens collected from several municipal hospitals in Shenyang during the period from October 2016 to January 2017 and identified by the BioMerieux ATB 1525 Expression Identification System.The drug resistance of clinical isolates of Acinetobacter baumannii were detected by K-B method.The phenotype of carbapenemase in multi-drug resistant Acinetobacter baumannii(MDR-AB)was detected by modified Hodge test,Carba NP test and EDTA synergy test.The carrying situation of OXA-23,NDM-1,In1 and Tn2009 genes was detected by PCR technique.The expression level of OXA-23 gene in carbapenem-sensitive and resistant strains was detected by RT-qPCR.Results42 MDR-AB strains and 9 pan-drug resistant AB(PDR-AB)strains were screened from 45 clinical isolates through drug susceptibility testing.The resistance rate of these MDR-AB strains to 16 representative antibiotics including quinolones,cephalosporins,aminoglycosides,β-lactams,carbapenems,penicillins and sulfo-namidesis was up to 80%,in which the resistance rate to carbapenem was more than 70%.36 carbapenemase-positive strains were detected from 42 MDR-AB strains by modified Hodge test and Carba NP test.No metallo-beta-lactamase strains were detected from 36 carbapenemase-positive strains by EDTA synergy test.The OXA-23,In1 and Tn2009 genes were amplified by PCR,while the NDM-1 gene was not amplified.RT-qPCR results showed that the expression level of OXA-23 gene in carbapenem-resistant AB was higher than that in sensitive strains.Conclusions(1)The drug resistance of AB isolated from this region was serious.All strains were resistant to cefoxitin and nitrofurantoin,while more sensitive to amikacin and tobramycin.Clinical rational use of drugs should be based on the results of drug sensitivity test,when necessary,combined with the results of molecular biology experiments.(2)NDM-1 gene was not detected in clinical isolates of Acinetobacter baumannii,indicating that NDM-1 positive AB has not yet been disseminated in this region.(3)OXA-23 gene mainly exists in chromosome of AB and plays a role in drug resistance,while plasmids of AB are more important as their media.(4)The drug resistance level of AB increases when OXA-23 and Tn2009 coexists in the same strain.When the three genes OXA-23,In1 and Tn2009 coexist,they increase the risk of drug resistance gene transfer.