耐碳青霉烯类鲍曼不动杆菌感染暴发的分子流行病学研究

目的分析某院耐碳青霉烯类鲍曼不动杆菌（CRAB）的分子流行病学特征和耐药机制，为预防和控制医院感染提供依据。方法对该院2010年1月-2012 年5月临床分离的32株CRAB，采用随机扩增多态性DNA法进行基因分型，并进行流行病学分析；通过改良Hodge试验和EDTA协同试验对碳青霉烯酶进行表型分析；检测外排泵抑制剂羰基氰氯苯腙（CCCP）对美罗培南最低抑菌浓度（MIC）的影响，筛选外排泵表型阳性菌株。结果32株CRAB检测出9种基因型，其中以A（10株）、H（7株）两种基因型为主，其次为I型（4株），B和E基因型各3株，其他基因型各有1或2株。2012年3-5月分离11株CRAB，10株为H(7株)和I(3株)两种基因型，1株为A型。21株（65.63%）CRAB检测到OXA 23特异性条带，且其在改良Hodge试验中均为阳性（包括2012年3-5月分离的11株CRAB）；除1株CRAB检测到NDM 1外，其余金属β 内酰胺酶基因检测均为阴性；CRAB在CCCP存在的条件下对美罗培南MIC仅有轻微改变，均为外排泵表型阴性。CRAB主要分布在重症监护室（13株）和神经外科（7株）。结论该院2012年3-5月间暴发了CRAB同一基因型克隆株的医院感染，鲍曼不动杆菌对碳青霉烯类药物耐药的主要机制是表达OXA 23；鲍曼不动杆菌对美罗培南耐药与外排泵无关，产NDM 1菌株已在该院出现。

Molecular epidemiologic characterization of infection outbreaks caused by carbapenem resistant Acinetobacter baumannii

ObjectiveTo investigate the epidemiologic characteristics and drug resistance mechanism of carbapenem resistant Acinetobacter baumannii （CRAB） isolated from a hospital, so as to guide prevention and control of healthcare associated infection（HAI）.MethodsA total of 32 CRAB strains isolated clinically from January 2010 to May 2012 were performed genotyping by randomly amplified polymorphic DNA fingerprinting, and epidemiological analysis was conducted; carbapenemase were screened by modified Hodge test and EDTA disk synergy test. The effect of efflux pump inhibitor carbonyl cyanide m chlorophenyl hydrazone （CCCP）on minimum inhibitory concentration of meropenem was detected, efflux pump positive strains were screened.Results32 CRAB strains displayed 9 kinds of genotypes, type A, H, I,B, E, and other types were 10,7,4,3,3,and 1-2 isolates respectively. From March to May,2012, 11 CRAB strains were isolated, type H,I,and A were 7,3, and 1 isolates respectively. 21 （65.63%） CRAB strains expressed oxacillinase （OXA 23）, and were positive in modified Hodge test （including 11 strains isolated in March May,2012）; Except 1 isolate was detected New Delhi Metallo 1（NDM 1）, all other strains were negative for metallo lactamase test; the presence of CCCP slightly changed the MIC of meropenem to CRAB,all were negative for phenotype of efflux pump. CRAB strains were mainly isolated from patients in intensive care unit（13 isolates） and neurology department（7 isolates）.ConclusionThe outbreak of HAI of the clone with identical genotype occurred in this ICU between March and May,2012. Carbapenem resistance mechanism of A. baumannii can be attributed to the expression of OXA 23, and meropenem resistance is not related to the efflux pump, CRAB strain expressing NDM 1 has been detected in this hospital.