猪源肠球菌中氟苯尼考耐药性调查及fexA基因环境研究

doi:10.16431/j.cnki.1671-7236.2018.06.035

摘要/Abstract

摘要：

本研究旨在调查猪场中肠球菌对氟苯尼考的耐药性，检测氟苯尼考耐药基因，并测定肠球菌中氟苯尼考耐药基因fexA的基因环境，从而分析其可能的传播机理。以四川某猪场分离鉴定的50株肠球菌为研究材料，开展分离株对氟苯尼考的药物敏感性试验。运用PCR技术检测分离株中氟苯尼考耐药基因cfr、fexB、fexA、floR和estDL136。运用热不对称性PCR（TAIL-PCR）技术获得fexA基因周围序列信息，分析其基因环境。运用反向PCR技术验证序列中环化结构的存在，同时运用交叉PCR技术检测20株猪源肠球菌fexA基因的基因环境。结果显示，在分离出的50株肠球菌中，有34株对氟苯尼考耐药（MIC ≥ 16 mg/L），耐药率为68%。PCR结果显示，20株含有fexA基因，28株含有fexB基因，14株同时含有这两种基因。TAIL-PCR和测序结果显示，分离株DKC5中fexA基因存在于12 945 bp的Tn554转座子中。Tn554转座子可形成环化结构，其中的重复序列可形成含有2 395 bp的环化结构。本试验结果表明，猪源肠球菌对氟苯尼考耐药率较高，主要由fexA和fexB基因介导，fexA基因存在于Tn554结构中。预测fexA基因是经两次插入整合后进入DKC5分离株基因组序列的，这为fexA基因的水平传播提供了遗传依据。

关键词: 肠球菌; 氟苯尼考; 耐药性; fexA基因; TAIL-PCR; 基因环境

Abstract:

This study was aimed to investigate the resistance of Enterococcus to florfenicol in pig farms and analyze the florfenicol resistance genes.Also,the gene environments of florfenicol resistant gene fexA in Enterococcus were determined to identify the underlying transmission mechanism.Fifty strains of Enterococcus isolated from a pig farm in Sichuan province were used as the research materials to perform the drug susceptibility test of florfenicol.The florfenicol resistance genes cfr,fexB,fexA,floR and estDL136 were detected by PCR.The information of gene environment of fexA gene was obtained by TAIL-PCR and further analyzed.In addition,the presence of cyclized structure in the sequence was verified by PCR.Meanwhile,the genetic environment of 20 fexA-positive isolates was confirmed by cross-PCR.The results showed that among the 50 strains of Enterococcus,34 were resistant to florfenicol (MIC ≥ 16 mg/L),with a resistant rate of 68%.PCR results showed that 20 strains contained fexA gene,28 strains contained fexB gene,and 14 strains contained both of the two genes.Besides,TAIL-PCR and sequencing showed fexA gene in isolated strain DKC5 was located in the 12 945 bp Tn554 transposon.In particular,the Tn554 transposon could form a cyclized structure and its repeating sequence could also form a local cyclized structure containing 2 395 bp.The resistance rate of Enterococcus from swine to florfenicol was high,and was mainly mediated by fexA and fexB genes.Specifically,fexA gene was located in the Tn554 structure.It was predicted that fexA gene was inserted into DKC5 strain genome sequence by two insertions,which provided a genetic basis for the horizontal transmission of fexA gene.

Key words: Enterococcus; florfenicol; resistance; fexA gene; TAIL-PCR; genetic environment

中图分类号:

S852.61

张平, 彭琳瑶, 徐昌文, 李云霞, 张安云. 猪源肠球菌中氟苯尼考耐药性调查及fexA基因环境研究[J]. 《中国畜牧兽医》, 2018, 45(6): 1700-1707.

ZHANG Ping, PENG Linyao, XU Changwen, LI Yunxia, ZHANG Anyun. Study on Florfenicol Resistance and fexA Genetic Environment in Enterococcus from Swine[J]. , 2018, 45(6): 1700-1707.

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