National Risk Assessment Laboratory for Antimicrobial Resistance of Animal Original Bacteria, College of Veterinary Medicine, South China Agricultural University, Guangzhou 510642, China.
Guangdong Key Laboratory for Veterinary Drug Development and Safety Evaluation, College of Veterinary Medicine, South China Agricultural University, Guangzhou 510642, China.
J Antimicrob Chemother. 2020 Jun 1;75(6):1424-1427. doi: 10.1093/jac/dkaa044.
To clarify the transmission mechanism of the blaCTX-M-64 gene between Escherichia coli and Salmonella isolates from food animals.
A total of 329 E. coli and 60 Salmonella isolates collected from food animals in 2016 were screened for the presence of blaCTX-M-64 genes. The blaCTX-M-64-positive isolates were typed and plasmid and chromosome DNA was sequenced to determine the genetic context of blaCTX-M-64 and the plasmid types present.
The blaCTX-M-64 gene was identified in only three E. coli isolates but was the predominant gene in the Salmonella isolates (n = 9). These 12 CTX-M-64-positive isolates were all resistant to ampicillin, cefotaxime, ceftiofur, ceftriaxone, ceftazidime and florfenicol and 9 were resistant to ciprofloxacin. The blaCTX-M-64 gene was located on transferable IncI2 plasmids and an IncHI2 plasmid in three E. coli and one Salmonella isolate, respectively. The remaining eight Salmonella isolates contained blaCTX-M-64 integrated into the chromosome. Different genetic contexts of blaCTX-M-64 genes were found among the 12 isolates: ISEcp1-blaCTX-M-64-orf477-A/C on IncI2 plasmids of 3 E. coli isolates; ΔISEcp1-blaCTX-M-64-orf477-A/C in the chromosome of 1 Salmonella isolate; and ISEcp1-blaCTX-M-64-orf477 on the IncHI2 plasmid and chromosome of 8 Salmonella isolates.
To the best of our knowledge, this is the first report of chromosomally encoded CTX-M-64 in Salmonella isolates. ISEcp1-mediated transposition is likely to be responsible for the spread of blaCTX-M-64 between different plasmids and chromosomes in Enterobacteriaceae especially E. coli and Salmonella.
阐明食品动物源大肠杆菌和沙门氏菌分离株中 blaCTX-M-64 基因的传播机制。
2016 年从食品动物中采集了 329 株大肠杆菌和 60 株沙门氏菌分离株，筛选 blaCTX-M-64 基因的存在。对 blaCTX-M-64 阳性分离株进行分型，并对质粒和染色体 DNA 进行测序，以确定 blaCTX-M-64 的遗传背景和存在的质粒类型。
仅在 3 株大肠杆菌分离株中鉴定出 blaCTX-M-64 基因，但该基因是沙门氏菌分离株（n=9）中的主要基因。这 12 株 CTX-M-64 阳性分离株均对氨苄西林、头孢噻肟、头孢噻呋、头孢曲松、头孢他啶和氟苯尼考耐药，9 株对环丙沙星耐药。blaCTX-M-64 基因位于可转移的 IncI2 质粒和 1 株大肠杆菌和 1 株沙门氏菌分离株的 IncHI2 质粒上。其余 8 株沙门氏菌分离株含有整合到染色体上的 blaCTX-M-64 基因。在这 12 株分离株中发现了 blaCTX-M-64 基因的不同遗传背景：3 株大肠杆菌分离株的 IncI2 质粒上的 ISEcp1-blaCTX-M-64-orf477-A/C；1 株沙门氏菌分离株的染色体上的ΔISEcp1-blaCTX-M-64-orf477-A/C；8 株沙门氏菌分离株的 IncHI2 质粒和染色体上的 ISEcp1-blaCTX-M-64-orf477。
据我们所知，这是沙门氏菌分离株中首次报道染色体编码的 CTX-M-64。ISEcp1 介导的转位可能是 blaCTX-M-64 在肠杆菌科，特别是大肠杆菌和沙门氏菌的不同质粒和染色体之间传播的原因。
