Beijing Advanced Innovation Center for Food Nutrition and Human Health, College of Veterinary Medicine, China Agricultural University, Beijing, China.
Public Health Agency of Sweden, Stockholm, Sweden.
J Antimicrob Chemother. 2018 Jul 1;73(7):1777-1780. doi: 10.1093/jac/dky110.
To characterize the mobile colistin resistance gene mcr-5 in Aeromonas hydrophila from backyard pigs in rural areas of China.
Pig faecal samples from 194 households were directly tested for the presence of mcr-5 by PCR assay and the phenotypic antimicrobial susceptibility profiles of the mcr-5-positive isolates were determined using the broth dilution method. The genomic location and transferability of mcr-5 were analysed by S1-PFGE with Southern blotting and DNA hybridization, and natural transformation, respectively. One strain isolated from an mcr-5-positive sample was subjected to WGS and the stability of the mcr-5-harbouring plasmid over successive generations was examined by subculturing.
One mcr-5-positive A. hydrophila isolate showing resistance, with a colistin MIC of 4 mg/L, was isolated from a backyard pig faecal sample. mcr-5 was located on a 7915 bp plasmid designated pI064-2, which could naturally transform into a colistin-susceptible A. hydrophila strain of porcine origin and mediated colistin resistance in both the original isolate and its transformants. The plasmid backbone (3790 bp) of pI064-2 showed 81% nucleotide sequence identity to the corresponding region of the ColE2-type plasmid pAsa1 from Aeromonas salmonicida, while similar replication primases are widely distributed among aeromonads, Enterobacteriaceae and Pseudomonas species.
To the best of our knowledge, this is the first identification of the novel colistin resistance gene mcr-5 in an A. hydrophila isolate from the faeces of a backyard pig. mcr-5 is expected to be able to disseminate among different bacterial species and genera.
研究中国农村地区后院猪源嗜水气单胞菌中移动多黏菌素耐药基因 mcr-5 的特征。
采用 PCR 法直接检测 194 户猪粪便样本中 mcr-5 的存在情况，采用肉汤稀释法测定 mcr-5 阳性分离株的表型抗菌药物敏感性谱。通过 S1-PFGE 结合 Southern 印迹杂交和 DNA 杂交分析 mcr-5 的基因组定位和可转移性，并分别通过自然转化分析 mcr-5 的可转移性。从 mcr-5 阳性样本中分离出一株菌进行 WGS 分析，并通过连续传代培养研究 mcr-5 携带质粒的稳定性。
从一株后院猪粪便样本中分离到一株 mcr-5 阳性嗜水气单胞菌，其对黏菌素的 MIC 为 4 mg/L。mcr-5 位于一个 7915 bp 的质粒上，命名为 pI064-2，该质粒可自然转化为一株对黏菌素敏感的猪源嗜水气单胞菌，并在原始分离株及其转化株中均介导对黏菌素的耐药性。pI064-2 的质粒骨架（3790 bp）与来自嗜水气单胞菌的 ColE2 型质粒 pAsa1 的相应区域有 81%的核苷酸序列同源性，而类似的复制启动子广泛分布于气单胞菌、肠杆菌科和假单胞菌属中。
据我们所知，这是首次在一株来自后院猪粪便的嗜水气单胞菌中发现新型黏菌素耐药基因 mcr-5。mcr-5 有望在不同的细菌种属间传播。
