He Tao, Wei Ruicheng, Zhang Lili, Sun Lichang, Pang Maoda, Wang Ran, Wang Yang
Jiangsu Key Laboratory of Food Quality and Safety-State Key laboratory Cultivation Base of MOST, Institute of Food Safety and Nutrition, Jiangsu Academy of Agricultural Sciences, Nanjing 210014, PR China.
Jiangsu Key Laboratory of Food Quality and Safety-State Key laboratory Cultivation Base of MOST, Institute of Food Safety and Nutrition, Jiangsu Academy of Agricultural Sciences, Nanjing 210014, PR China.
Vet Microbiol. 2017 Aug;207:153-158. doi: 10.1016/j.vetmic.2017.06.010. Epub 2017 Jun 13.
The aim of this study was to investigate the prevalence of bla gene in Escherichia coli isolates from dairy cows and to characterize the molecular traits of the bla-positive isolates. A total of 169 cows were sampled (169 feces and 169 raw milk samples) in three dairy farms in Jiangsu Province and 203 E. coli isolates were recovered. Among these strains, three isolates carried bla gene, including one co-harboring mcr-1, which belonged to sequence type 446 and the other two belonged to ST2. Susceptibility testing revealed that the three bla-positive isolates showed extensive resistance to antimicrobials. The bla gene was located on a ∼46-kb IncX3 transferrable pNDM-MGR194-like plasmid in all three isolates, while mcr-1 was located on a ∼260-kb IncHI2 plasmid pXGE1mcr. Competition experiments revealed that acquisition of bla or mcr-1-bearing plasmid can incur fitness cost of bacterial host, however, plasmid stability testing showed that both bla and mcr-1-carrying plasmid maintained stable in the hosts after ten passages without antimicrobial selection. Whole genome sequencing revealed that the mcr-1 gene coexisted with multiple resistance genes in pXGE1mcr and the backbone of this plasmid was similar to that of previously reported mcr-1-positive plasmid pHNSHP45-2. Moreover, pXGE1mcr could be conjugated into clinical NDM-5-positive E. coli isolates in vitro, thereby generating strains that approached pan-resistance. Active surveillance efforts are imperative to monitor the prevalence of bla and mcr-1 in carbapenem-resistant Enterobacteriaceae from dairy farms throughout China.
本研究旨在调查奶牛源大肠杆菌分离株中bla基因的流行情况，并对bla阳性分离株的分子特征进行表征。在江苏省的三个奶牛场共采集了169头奶牛的样本（169份粪便和169份生鲜乳样本），并分离出203株大肠杆菌。在这些菌株中，有三株携带bla基因，其中一株同时携带mcr-1，属于序列型446，另外两株属于ST2。药敏试验表明，这三株bla阳性分离株对多种抗菌药物表现出广泛耐药。在所有三株分离株中，bla基因位于一个约46 kb的IncX3型可转移pNDM-MGR194样质粒上，而mcr-1位于一个约260 kb的IncHI2质粒pXGE1mcr上。竞争实验表明，获得携带bla或mcr-1的质粒会使细菌宿主产生适应性代价，然而，质粒稳定性测试表明，在没有抗菌药物选择的情况下传代十次后，携带bla和mcr-1的质粒在宿主中均保持稳定。全基因组测序表明，mcr-1基因在pXGE1mcr中与多个耐药基因共存，该质粒的骨架与先前报道的mcr-1阳性质粒pHNSHP45-2相似。此外，pXGE1mcr在体外可接合到临床NDM-5阳性大肠杆菌分离株中，从而产生接近泛耐药的菌株。必须积极开展监测工作，以监测bla和mcr-1在中国各地奶牛场耐碳青霉烯类肠杆菌科细菌中的流行情况。
