对碳青霉烯类抗生素敏感性降低的肠杆菌科细菌产酶机制分析

Analysis of the carbapenemase- producing mechanism of Enterobacteriaceae with decreased susceptibility to carbapenems

了解临床分离肠杆菌菌种分布及对碳青霉烯类抗菌药物的耐药现状和分子机制。方法 收集四川大学华西医院2009~2010 年分离到的对碳青霉烯类药物敏感性降低的肠杆菌科非重复菌株共 45 株，测定其对常用抗菌药物的最低抑菌浓度（MIC）以及产酶表型和PCR检测产酶分子机制。结果 对碳青霉烯类药物敏感性降低的45株肠杆菌科细菌中，17株菌对亚胺培南中介或耐药，21株对美罗培南中介或耐药，36株对厄他培南中介或耐药，绝大多数菌株对头孢菌素类耐药。受试菌株中改良Hodge试验阳性检出率最高（77.8%），其次为EDTA纸片增效试验（57.8%）和PBA纸片增效试验（22.2%）。blaTEM、blaSHV和blaCTX-M基因检出率分别为60.0%，53.3%和15.6%，同时携带2种及以上基因的检出率为44.4%。blaIMP基因检出率为48.9%。4株菌（3株产酸克雷伯菌，1株阴沟肠杆菌）为blaKPC基因阳性，检出率为8.9%，且位于质粒上。结论 研究发现肠杆菌科细菌产酶是对碳青霉烯类药物敏感性下降的主要机制，产碳青霉烯酶或合并多种β-内酰胺酶可引起非敏感或耐药的出现。本研究报道了在西南地区发现在质粒携带的KPC-2型酶，可能引起不同菌种间水平传播，需引起足够重视。

Objectives To analyze the distribution of Enterobacteriaceae isolated from West China Hospital, investigate the antibiotic resistance profile of Enterobacteriaceae with decreased susceptibility to carbapenems and explore the molecular mechanism. Methods Forty-five Enterobacteriaceae strains resistant or with reduced susceptibility to carbapenems were isolated from patients in West China Hospital. The antimicrobial susceptibility and carbapenemase-producing phenotypes of the bacteria were examined and specific PCR were performed to determine the molecular mechanism. Results Of the 45 isolates, 17, 21 and 36 were resistant or intermediate strains to imipenem, meropenem and ertapenem, respectively. The majority of these isolates showed resistance to cephalosporins. The modified Hodge test resulted in the highest positivity rate （77.8%）, followed by EDTA disc test （57.8%） and PBA disc test （22.2%）. BlaTEM, blaSHV and blaCTX-M were detected in 60.0%, 53.3% and 15.6% of these strains with reduced susceptibility. The rate of strains carrying 2 or more genes was 44.4%, and the detection rate of blaIMP was 48.9%. BlaKPC was identified in 4 （8.9%） high-level resistant strains and confirmed to locate on the plasmid. Conclusion Production of carbapenemase contributes to reduced susceptibility of carbapenems in Enterobacteriaceae. The presence of blaKPC, MBL and ESBL, and their possible combinations can be the main factor contributing to carbapenem resistance or reduced susceptibility in Enterobacteriaceae. The KPC-2 carbapenemase gene located on the plasmids we found in this study can cause potential horizontal transmission across strains.