Clonal spread of <i>Escherichia coli</i> O101:H9-ST10 and O101:H9-ST167 strains carrying <i>fosA3</i> and <i>bla</i><sub>CTX-M-14</sub> among diarrheal calves in a Chinese farm, with Australian <i>Chroicocephalus</i> as the possible origin of <i>E. coli</i> O101:H9-ST10
Wan-Yun He, 华南农业大学兽医学院，广东 广州 510642，中国, Xingxing Zhang, Guolong Gao, Ming-Yi Gao, Fagang Zhong, Luchao Lv, Zhongpeng Cai, Xingfeng Si, Jun Yang, Jian–Hua Liu, 岭南现代农业科学与技术广东省实验室，广东 广州 510642，中国, 新疆农垦科学研究院绵羊遗传改良与健康养殖国家重点实验室，畜牧兽医研究所，新疆 石河子 832000，中国, 浙江天童森林生态系统国家野外科学观测研究站，生态与环境科学学院，华东师范大学，上海 200241，中国
Abstract
During a 2018 antimicrobial resistance surveillance of <i>Escherichia coli</i> isolates from diarrheal calves in Xinjiang Province, China, an unexpectedly high prevalence (48.5%) of fosfomycin resistance was observed. This study aimed to reveal the determinants of fosfomycin resistance and the underlying transmission mechanism. Polymerase chain reaction (PCR) screening showed that all fosfomycin-resistant <i>E. coli</i> carried the <i>fosA3</i> gene. Pulsed-field gel electrophoresis (PFGE) and southern blot hybridization revealed that the 16 <i>fosA3</i>-positive isolates belonged to four different PFGE patterns (i.e., A, B, C, D). The <i>fosA3</i> genes of 11 clonally related strains (pattern D) were located on the chromosome, while others were carried by plasmids. Whole-genome and long-read sequencing indicated that the pattern D strains were <i>E. coli</i> O101:H9-ST10, and the pattern C, B, and A strains were O101:H9-ST167, O8:H30-ST1431, and O101:H9 with unknown ST, respectively. Among the pattern C strains, the <i>bla</i><sub>CTX-M-14</sub> gene was co-localized with the <i>fosA3</i> gene on the F18:A-:B1 plasmids. Interestingly, phylogenetic analysis based on core genome single nucleotide polymorphisms (cgSNPs) showed that the O101:H9-ST10 strains were closely related to a Australian-isolated <i>Chroicocephalus</i>-origin <i>E. coli</i> O101:H9-ST10 strain producing CTX-M-14 and FosA3, with a difference of only 11 SNPs. These results indicate possible international dissemination of the high-risk <i>E. coli</i> clone O101:H9-ST10 by migratory birds.