质粒介导的志贺菌产超广谱β内酰胺酶及其耐药基因型

Study on plasmid-mediated extended spectrum β-lactamases and their resistance phenotypes in Shigella

目的探讨产生超广谱β内酰胺酶（ESBLs）志贺菌的特性及与耐药质粒的关系。方法用K-B法做药敏试验并筛选可疑产ESBLs志贺菌株；ESBLs表型确证试验检测可疑产ESBLs志贺菌；采用TEM、SHV、CTX—M-1组、CTX—M-2组、CTX—M-9组B内酰胺酶通用引物进行PCR检测，TEM、CTX—M-9组全编码基因引物进行PCR测定，对扩增产物进行DNA序列分析；对产ESBLs志贺菌进行接合传递试验，供体菌和接合子用稀释法进行MIC测定。结果在275株志贺菌中有12株为产ESBLs志贺菌，其中8株志贺菌基因型为CTX—M-14型，4株为CTX—M-3型；产ESBLs志贺菌接合传递试验全部阳性，其接合子只对B内酰胺类抗生素耐药。结论本地区志贺菌对B内酰胺类抗生素的严重交叉耐药是由ESBLs所致，产ESBLs志贺菌可通过质粒传递耐药性。

Objective To discuss the characteristics of extended-spectrum beta-lactamases （ESBLs）-producing Shigella and the relation between them and drug-resistance plasmid. Methods The suspicious ESBLs-producing isolates were screened by K-B disc diffusion method, and the ESBLs-producing strains were confirmed by confirmatory test recommended by the National Committee for Clinical Laboratory Standards. Furthermore, the partial blagere of these isolates were detected by PCR using universal primers for TEM, SHV, CTX-M-1 group, CTX-M-2 group and CTX-M-9 group, respectively. The entire blaCTX-M-9 and blawEM were amplified by PCR using the primers outside the open reading frame （ORF） of these β-lactamases and products were directly sequenced. The conjugation experiment was performed to determine whether the resistance was transferable. Minimal inhibitory concentration （MIC） was detected with double agar dilution method. Results Of the 275 isolates, 12 strains were identified as ESBLs producers. Among them, 8 strains were CTX-M-14 carriers and 4 strains were CTX-M-3 carriers. All ESBLs-producing isolates are positive for plasmid conjugative transfer test. The transconjugants are only resistance to beta-lactams. Conclusions High resistance to beta-lactams in Shigella is caused by production of ESBLs in the local area. The ESBLs-producing isolates can transfer the drug resistance through lateral transfer of plasmid.