In recent years, there have been increased reports on the detection of extended-spectrum beta-lactamase (ESBL)-producing Escherichia coli and Salmonella strains from food-producing animals and animal products in the United States. We characterized 18 ESBL E. coli isolates from cattle (n = 5), chicken breast (n = 5), ground turkey (n = 6), ground beef (n = 1), and pork chops (n = 1) that were collected by the National Antimicrobial Resistance Monitoring System (NARMS) between 2011 and 2015. In vitro antimicrobial susceptibility testing was done against a panel of 14 antimicrobials followed by a secondary panel of 9 β-lactam agents. Whole-genome sequencing was used to characterize the resistome, plasmids, and the genetic structures of the ESBL genes. All ESBL-producing E. coli isolates were resistant to at least three antimicrobial classes and carried various blaCTX-M genes. Most of the cattle and ground turkey isolates carried blaCTX-M-27. In chicken breast isolates, blaCTX-M-1 was present as part of an ISEcp1 transposition unit carried on a plasmid that shares sequence similarity with the backbone structure of the IncI plasmid. Isolates carrying the blaCTX-M-14 and blaCTX-M-15 genes, widely distributed in human clinical isolates, were also isolated. To our knowledge, this is the first report of the widely distributed blaCTX-M-14 and blaCTX-M-15 in E. coli isolates from retail meat samples in the United States. Different insertional sequences were identified upstream of these blaCTX-Ms, including ISEcp1, IS26, and IS903-D. CTX-M in E. coli from food animals and retail chicken breast were often present on plasmids with other resistance genes. Other resistance genes identified included aadA, strA, strB, aac(3)-IId, aac(3)-VIa, aph(3')-Ic, blaTEM, blaHERA-3, floR, sul1, sul2, catA1, tetA, tetB, dfrA, and qacE. These data describe the emergence of CTX-M-carrying E. coli isolates in food animals and animal products monitored by NARMS program.
Keywords: CTX-M; ESBL; Escherichia coli.