Fecal Carriage and Genetic Characterization of CTX-M-1/9/1-Producing Escherichia coli From Healthy Humans in Hangzhou, China

CTX-M-199, a novel chimeric β-lactamase which mediated resistance to sulbactam and tazobactam, was recently identified in Hangzhou, China. This study investigated the prevalence of fecal carriage of bacteria producing CTX-M-199 and other CTX-M-1/9/1-type enzymes among healthy individuals and characterized the genetic features of blaCTX–M–1/9/1-bearing mobile elements. A total of 74 Enterobacterales strains carrying various blaCTX–M–1/9/1 genes, including blaCTX–M–64 (n = 40, carriage rate of 0.74%), blaCTX–M–199 (n = 23, 0.40%), blaCTX–M–123 (n = 5, 0.10%), novel blaCTX–M–153 (n = 5, 0.10%), and blaCTX–M–132 (n = 2, 0.04%), were isolated from 68 out of 5,000 (1.36%) fecal samples of healthy adults in Hangzhou City. Phylogenetic analysis based on whole-genome sequencing data showed that 72 blaCTX–M–1/9/1-bearing Escherichia coli isolates were clustered into four major clades, three of which included CTX-M-199 producers. Sixty out of 75 blaCTX–M–1/9/1 genes were located on plasmids belonging to four Inc types: IncI2, IncI1, IncFIB, and IncHI2. The blaCTX–M–199 genes were harbored by three of the four types of plasmids except for IncHI2. All these blaCTX–M–1/9/1 genes were carried on an ISEcp1-mediated transposition unit. In conclusion, human fecal carriage of blaCTX–M–1/9/1 was low in healthy populations of China. The ISEcp1 was commonly associated with blaCTX–M–1/9/1 and may mediate its transmission on various mobile elements. Our findings provide insights into the dissemination and the development of further measures for the control of pathogens producing CTX-M-1/9/1-type enzymes.