Department of Comparative Biomedical Sciences, College of Veterinary Medicine, Mississippi State University, Mississippi State, Mississippi.
Department of Comparative Biomedical Sciences, College of Veterinary Medicine, Mississippi State University, Mississippi State, Mississippi.
J Glob Antimicrob Resist. 2023 Jun;33:177-185. doi: 10.1016/j.jgar.2023.03.005. Epub 2023 Mar 21.
Edwardsiella ictaluri is an important pathogen in farmed raised catfish. Recently, we showed that resistance to tetracycline and florfenicol in the E. ictaluri MS-17-156 strain isolated from channel catfish was facilitated by acquisition of a 135 kb plasmid (named pEIMS-171561).
We described the genetic structure of pEIMS-171561. Plasmid copy number and stability within E. ictaluri strain MS-17-156 was determined. We also investigated the in vitro and in vivo transferability of pEIMS-171561 using catfish as a model for in vivo transfer.
pEIMS-171561 belonged to the IncA/C group and contained florfenicol efflux major facilitator superfamily (MFS) (floR), sulfonamides (sul2), and tetracycline efflux MFS (tetD) genes. The plasmid contained two conjugative transfer-associated regions and encoded six transposases and insertion sequences. In vitro conjugation experiments demonstrated that the IncA/C plasmid can transfer from E. ictaluri to Escherichia coli. The plasmid was stable in E. ictaluri without selection pressure for 33 days. We showed that pEIMS-171561 did not transfer from E. ictaluri MS-17-156 to endogenous microbiota in catfish. Moreover, we could not detect in vivo conjugal transfer of pEIMS-171561 from E. ictaluri to E. coli. Results from real-time PCR revealed upregulation of the floR gene in the intestines of catfish receiving florfenicol-medicated feed, compared with that in catfish receiving unmedicated feed.
This study demonstrated that pEIMS-171561 did not disseminate from E. ictaluri to gut microbiota under selective pressure. This result suggests a limited role of the fish microbiota as a reservoir for this plasmid and for the spread of resistance.
爱德华氏菌是养殖鲶鱼的重要病原体。最近，我们发现从斑点叉尾鮰中分离的爱德华氏菌 MS-17-156 菌株对四环素和氟苯尼考的耐药性是由获得一个 135kb 的质粒（命名为 pEIMS-171561）引起的。
我们描述了 pEIMS-171561 的遗传结构。测定了质粒在爱德华氏菌 MS-17-156 菌株中的拷贝数和稳定性。我们还使用鲶鱼作为体内转移模型，研究了 pEIMS-171561 的体外和体内可转移性。
pEIMS-171561 属于 IncA/C 组，包含氟苯尼考外排主要易化超家族（MFS）（floR）、磺胺类（sul2）和四环素外排 MFS（tetD）基因。该质粒包含两个可接合转移相关区域，并编码六个转座酶和插入序列。体外接合实验表明，IncA/C 质粒可以从爱德华氏菌转移到大肠杆菌。在没有选择压力的情况下，质粒在爱德华氏菌中稳定 33 天。我们表明，pEIMS-171561 不会从爱德华氏菌 MS-17-156 转移到鲶鱼的内源性微生物群。此外，我们无法检测到 pEIMS-171561 从爱德华氏菌到大肠杆菌的体内共轭转移。实时 PCR 结果显示，接受氟苯尼考给药饲料的鲶鱼肠道中 floR 基因的表达上调，而接受未给药饲料的鲶鱼肠道中则没有上调。
本研究表明，在选择压力下，pEIMS-171561 不会从爱德华氏菌转移到肠道微生物群。这一结果表明，鱼类微生物群作为该质粒和耐药性传播的储存库的作用有限。
