摘要
      对甲氧苄啶的耐药性主要是通过获得可移动的dfrA基因介导的，其中大多数是在肠杆菌中发现的。2014年至2020年，共从中国不同农场采集了139株鸭疫里默氏菌分离株。鸭疫病毒分离株的全基因组测序（WGS）和基因组分析显示，有一个504bp的开放阅读框（ORF）编码一个推定的dfrA基因。该DfrA变体与DfrA36具有66.47%的氨基酸序列同一性，与任何其他先前鉴定的DfrA蛋白具有≤51.20%的同一性。新的dfrA基因被命名为dfrA49，当被克隆到大肠杆菌BL21（DE3）中时，赋予了甲氧苄啶（TMP）抗性。从江苏和广东省分离到30株dfrA49阳性菌株（分别为5/38，13.16%和25/101，24.75%）。38个分离株中有5个获得了完整的基因组序列。基因组分析显示，dfrA49基因位于染色体或质粒上（其中四个位于染色体上，一个位于质粒上）。质粒p20190305E2-2_2携带dfrA49、catB、ermF、ereD、blaOXA（与blaOXA-29的同一性为88.36%）、Δarr和tet（X18）。进一步的研究表明，鸭疫霉中dfrA49通常与catB共存。在本研究中，利用WGS和生物信息学方法，在鸭疫霉的染色体和质粒序列中鉴定并表征了一个新的甲氧苄啶抗性基因dfrA49。它进一步扩展了对甲氧苄啶产生耐药性的可移动dfrA基因库的知识，并提供了关于鸭疫霉抗生素耐药性基因的信息，在鸭疫霉中，耐药性基因库的循环尚不清楚。
ABSTRACT
Resistance to trimethoprim is mainly mediated by the acquisition of mobile dfrA genes, and most of them were discovered in Enterobacteriales. A total of 139 Riemerella anatipestifer isolates were collected from different farms in China during 2014 to 2020. Whole genome sequencing (WGS) and genome analysis of R. anatipestifer isolates revealed a 504-bp open reading frame (ORF) encoding a putative dfrA gene. This DfrA variant shared 66.47% amino acid sequence identity with DfrA36 and shared ≤51.20% identity with any other previously identified DfrA proteins. The novel dfrA gene, designated dfrA49, conferred trimethoprim (TMP) resistance when cloned into Escherichia coli BL21(DE3). Thirty dfrA49-positive isolates were identified from Jiangsu and Guangdong province (5/38, 13.16%, and 25/101, 24.75%, respectively). Five of the 38 isolates had obtained the complete genome sequences. Genomic analysis showed that the dfrA49 gene was located on chromosomes or a plasmid (four of them were on chromosomes and one was located on a plasmid). The plasmid p20190305E2-2_2 carried dfrA49, catB, ermF, ereD, blaOXA (88.36% identity with blaOXA-209), Δarr, and tet(X18). Further research indicated that dfrA49 usually coexisted with catB in R. anatipestifer. In this study, a novel trimethoprim resistance gene, dfrA49, was identified and characterized in chromosome and plasmid sequences from R. anatipestifer using WGS and bioinformatic methods. It further expands knowledge about the pool of mobile dfrA genes that confer resistance to trimethoprim and provides information about antibiotic resistance genes in R. anatipestifer, where the resistance gene pool circulating is not well understood.

https://journals.asm.org/doi/full/10.1128/spectrum.04747-22