| AbstractObjective: To assess the clinical distribution and antibacterial resistance from the clinical isolates of Acinetobacter baumannii(AB), To evaluate the differences among tigecycline susceptibility testing methods for Acinetobacter baumannii.Analyze the resistance genes and the molecular epidemiological typing of tigecycline resistant isolates.While provide informations to clinical for controlling the infection and transmission of tigecycline resistant strains.Methods: The minimal inhibitory concentration(MICs) of 24 kinds of antimicrobial drugs against 119 clinical Acinetobacter baumannii isolates were determined by agar dilution method.Tigecycline susceptibilities were tested by the broth microdilution, agar dilution and disk diffusion. The chromosomal DNA was amplified by PCR using primers of efflux pumps genes(ade ABC-ade RS), the expression of efflux pump genes(ade A, ade B, ade C) were determined by Real Time-PCR.The tetracycline resisitance genes(tet A,tet B),class D carbapenemase-encoding genes(OXA-23 、 OXA-51) and class 1 integrons were detected by PCR in 119 A.baumannii isolates, the homology analysis of tigecyclineresistant isolates.Results: A total of 119 clinical A.baumannii isolates mainly in sputum(75.32%)type.Distributed in respiration(30.3%),ICU(26.1%),neurosurgery(12.6%).Strains isolated almost from aged male patients.All isolates were fully susceptible to polymyxin B. The resistance rates of the isolates to tigecycline is about 10% by agar dilution method. The incidence of multidrug resistance was 76.5%(91/119).In vitro susceptibility of tigecycline was tested by broth microdilution, agar dilution and disk diffusion against 119 A.baumannii isolates,resistance rates were0.0%(0/119)、11.7%(14/119)and 4.2%(5/119)according to FDA(Food and Drug Administration)criteria,resistance rates were 0.0%( 0/119)、 45.4%( 54/119)、36.2%(43/119)according to EUCAST(European Committee on Antimicrobial susceptibility testing) criteria.A total of 91 multidrug resistant strains include 10 tigecycline non-susceptible A.baumannii TNAB(10/119) and 81 tigecycline susceptible A.baumannii TSAB(81/91). In non-susceptible group(TNAB) the detection rate of ade ABC-RS were 100%,in susceptible group(TSAB) the detection rate of ade ABC-RS were76.5%.The relative expression of ade A and ade C in TNAB group was higher than that in TSAB group,also the differences were statistically significant.But the relative expression of ade B in TNAB and TSAB group the differences were not statisticallysignificant.In tigecycline non-susceptible group(TNAB) the detection rate of OXA-23 、OXA-51 and int I were 100% 、 100% and 90%.In tigecycline susceptible group(TSAB) the detection rate of OXA-23、OXA-51 and int I were 35.8%、100% and76.5%.By MLST, A total of 9 different sequence types(ST),of which 5 novel STs are newly identified. Calculations by e BRUST software indicates that ST138(1-3-3-2-2-50-3) is the dominant STs.Conclusion:1.Since 76.5%(91/119) clinical isolates of A.baumannii were multidrug-resistant.Imipenem and meropenem as traditional antimicrobial drugs,have a high resistance rate,while tigecycline which have lower resistance rate are potent therapies against infections caused by multidrug-resistant A.baumannii. Therefore it is necessary to keep the susceptibility frequently monitored.2.As a novel Glycylcycline of clinical antibiotics, there is neither any standardized criteria nor methods, which announced by CLSI, about the test on susceptibilities of tigecycline. And there has a remarkable difference among three methods recommended by CLSI. An uniform standard should be established for providing accurate basis to clinical diagnosis and therapies against pathogens.3.Ade ABC active efflux system plays a significant role in mediating A.baumannii resistance to tigecycline. OXA-23, OXA-51 and int I exist widely in tigecycline-resistant A.baumannii. The tigecycline resistance rate in OXA-23 positive strains is significantly higher than that in OXA-23 negative strains(P<0.01), it is indicated that OXA-23 is involved in tigecycline resistance to A.baumannii.4.Tips of MLST results: corresponding departments, which had isolated TNAB strains, shall perform well on hand hygiene, aseptic operation and bedside segregation of infectious patients. For controlling the nosocomial infection and transmission of tigecycline non-susceptible A.baumannii. |
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