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Dissemination of antimicrobial resistance in food animals is a One Health concern, but sheep production has been overlooked. This study aimed to explore the dissemination of Escherichia coli resistant to extended-spectrum cephalosporins (ESC) in feedlot lambs. Two pens were sampled on two occasions, and carcasses and other mammals living around were also tested. E. coli were recovered and antibiotic resistance determined. bla CTX-M/CMY genes and their genetic localization were characterized. Whole genome sequencing (WGS) was performed to confirm clonal relationship. The most prevalent ESC-resistance genes in the 108 E. coli isolates were bla CTX-M-55 (53.7 %), bla CTX-M-2 (14.8 %) and bla CMY-2 (13.9 %). Most bla CTX-M-55 genes were found on the chromosome, but IncA/C, IncHI1, IncHI2 and IncF plasmids were also identified. Genetic diversity was observed even though ST6448 was by far the most frequent ST. WGS analysis showed high similarity among isolates recovered from feedlot lambs, animals in the surroundings and lambs' carcasses, proving the clonal and plasmidic dissemination., Competing Interests: Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper. None., (Copyright © 2024 Elsevier Ltd. All rights reserved.)

Extended-spectrum cephalosporin (ESC) resistance remains a threat since ESC are important antimicrobials used to treat infections in humans and animals. Escherichia coli is an important source of ESC-resistance genes, such as those encoding extended-spectrum β-lactamases (ESBLs). E. coli is a common commensal of lambs. Reports that contaminated food can be a source of ESC-resistant bacteria in humans and that ESBL-producing E. coli are found in sheep in Brazil led us to survey their presence in retail lamb meat. Twenty-five samples intended for human consumption were screened for ESC-resistant E. coli , and the isolates were characterized. IncI1- bla CTX-M-8 and IncHI2- bla CTX-M-2 were the main plasmids responsible for ESC resistance. The plasmids harbored common ESBL genes in Enterobacteriaceae from food-producing animals in Brazil. IncI1- bla CTX-M-14 and IncF- bla CTX-M-55 plasmids, associated with human infections, were also detected. Few CTX-M-producing E. coli have been clustered by typing methods, and some may be genetically pathogenic. The findings indicate the presence of diverse strains of E. coli , harboring important ESBL genes, in lamb meat in Brazil. Surveillance of ESC-resistant bacteria could reduce the spread of antimicrobial resistance through the food chain.