Dissemination of Multidrug-Resistant Commensal Escherichia coli in Feedlot Lambs in Southeastern Brazil

Abstract

Antimicrobial resistance (AR) is a public health issue since it limits the choices to treat infections by <i>Escherichia coli</i> in humans and animals. In Brazil, the ovine meat market has grown in recent years, but studies about AR in sheep are still scarce. Thus, this study aims to investigate the presence of AR in <i>E. coli</i> isolated from lambs during feedlot. To this end, feces from 112 lambs with 2 months of age, after weaning, were collected on the first day of the animals in the feedlot (day 0), and on the last day before slaughtering (day 42). Isolates were selected in MacConkey agar supplemented with 4 mg/L of ceftiofur and identified by biochemical methods. Isolates were submitted to an antimicrobial susceptibility test by disc-diffusion and PCR to investigate genes for phylogenetic group, virulence determinants and resistance to the several antimicrobial classes tested. The genetic localization of the <i>bla</i> genes detected was elucidated by S1-PFGE followed by Southern blot-hybridizations. The isolates were typed by <i>XbaI</i>-PFGE and MLST methods. Seventy-eight <i>E. coli</i> were isolated from 8/112 (7.1%) animals on day 0, and from 55/112 (49.1%) animals on day 42. Since only <i>fimH</i> was present in almost all <i>E. coli</i> (97.4%) as a virulence gene, and also 88.5% belonged to phylogroups B1 or A, we consider that isolates represent intestinal commensal bacteria. The dendrogram separated the 78 non-virulent isolates in seven clusters, two of which comprised 50 <i>E. coli</i> belonging to ST/CC 1727/446 or ST 3994 recovered on day 42 commonly harboring the genotype <i>bla</i> _{CMY -2}-<i>aac(3)-IIa</i> -<i>tetA</i>-<i>sul1</i>-<i>sul2</i>-<i>floR</i>-<i>cmlA</i>. Special attention should be given to the presence of <i>bla</i> _CTX-M-15, a worldwide gene spread, and <i>bla</i> _CTX-M-14, a hitherto undetected gene in <i>Enterobacteriaceae</i> from food-producing animals in Brazil. Importantly, <i>E. coli</i> lineages and plasmids carrying <i>bla</i> genes detected here have already been reported as sources of infection in humans either from animals, food, or the environment, which raises public health concerns. Hence, two types of commensal <i>E. coli</i> carrying important AR genes clearly prevailed during feedlot, but lambs are also reservoirs of bacteria carrying important AR genes such as <i>bla</i> _CTX-M-14 and <i>bla</i> _CTX-M-15, mostly related to antimicrobial treatment failure.