Wang Dongguo, Liang Haiyan, Chen Jiayu, Mou Yonghua, Qi Yongxiao
1 Department of Clinical Lab Medicine, Taizhou University affiliated Taizhou Municipal Hospital , Taizhou, China .
Microb Drug Resist. 2014 Oct;20(5):392-8. doi: 10.1089/mdr.2013.0201. Epub 2014 Mar 31.
Novel mdfA gene variants were identified simultaneously from 3 of 13 positive isolates of PCR amplification in Escherichia coli from patients. These 13 positive isolates showed resistance to chloramphenicol, tetracycline, and erythromycin. The 3 mdfA gene variants were of the same genotype and all the 13 positive isolates were investigated by conjugation experiment, EcoRI restriction, and gene mapping. Conjugation experiments demonstrated that the novel mdfA variant and mdfA genes were located on plasmids that were restricted by EcoRI for ∼8.2 kb-length, which was also validated by gene mapping. Further study indicated three types of genetic structures (A, B, and C) in the recombinant plasmids harboring mdfA and surrounding genes, and structure B was first reported in the article. Structure A comprises two partial-length and six full-length genes, including the mdfA gene variant in the recombinant plasmid; structure B comprises four full-length genes, the mdfA, ybjG, dacC, and ybjI; structure C comprises two full-length genes, the mdfA and dacC. These results suggested that the mdfA gene can function as transporter responsible for multidrug resistance and also mediated the synergistic function with its surrounding genes in conjugative plasmids.
在来自患者的大肠杆菌中，13株PCR扩增阳性分离株中有3株同时鉴定出新型mdfA基因变体。这13株阳性分离株对氯霉素、四环素和红霉素耐药。对这3种mdfA基因变体进行了相同基因型分析，并通过接合实验、EcoRI酶切和基因定位对所有13株阳性分离株进行了研究。接合实验表明，新型mdfA变体和mdfA基因位于受EcoRI酶切的约8.2 kb长度的质粒上，基因定位也证实了这一点。进一步研究表明，携带mdfA及其周围基因的重组质粒存在三种遗传结构类型（A、B和C），其中结构B在本文中首次报道。结构A包含两个部分长度基因和六个全长基因，包括重组质粒中的mdfA基因变体；结构B包含四个全长基因，即mdfA、ybjG、dacC和ybjI；结构C包含两个全长基因，即mdfA和dacC。这些结果表明，mdfA基因可作为负责多药耐药性的转运蛋白发挥作用，并且还介导了其在接合质粒中与其周围基因的协同功能。
