Conventionally Reared Wallon Meat Lambs Carry Transiently Multi-Drug-Resistant Escherichia coli with Reduced Sensitivity to Colistin Before Slaughter.

Simple Summary: Public health concerns continue about the spread of colistin resistance, especially after the discovery of the mobile colistin resistance (mcr) gene in Eschierichia coli a decade ago, which could potentially transfer resistance to other bacteria, posing risks to humans, animals and the environment. This study investigated the presence of colistin-resistant and ESBL-producing E. coli in both conventional indoor and organic outdoor Wallon meat lambs from birth to slaughter. Assessing n = 109 fecal samples in 2020 and 2021, 15% of E. coli isolates from conventional sheep showed reduced sensitivity to colistin, and 8% of these were multi-resistant. Genetic analysis showed the resistance was due to chromosomal mutations rather than the mcr-1 gene. In contrast, no resistant E. coli was isolated from the n = 32 samples from organic sheep, potentially due to different husbandry practices. The results highlight the importance of careful antimicrobial use and strict hygiene during slaughter to minimize risks to consumers, aligning with the One Health approach. Major efforts have been made to reduce the use of colistin in livestock since the discovery of the plasmid-borne mobile colistin resistance (mcr) gene in E. coli a decade ago, to curb the burden of its potential transmission to other bacterial species, spread between animals, humans and the environment. This study explored the longitudinal prevalence and characteristics of colistin-resistant and extended-spectrum beta-lactamase-producing (ESBL) E. coli via in vivo fecal and ex vivo carcass swabs from two batches of conventional indoor and organic outdoor Wallon meat sheep from birth to slaughter in 2020 and 2021. Antimicrobial susceptibility testing via broth microdilution revealed that n = 16/109 (15%) E. coli isolates from conventional meat lamb fecal samples had a reduced colistin sensitivity (MIC = 0.5 μg/mL) and thereof, n = 9/109 (8%) were multi-drug-resistant E. coli, while no resistant isolates were recovered from their carcasses. Sequencing revealed causative pmrB genes, indicating that the reduced sensitivity to colistin was not plasmid-borne. While the sample size was small (n = 32), no colistin-resistant and ESBL-producing E. coli were isolated from the organic meat sheep and their carcasses, potentially due to the different husbandry conditions. Prudent and judicious antimicrobial use and strict slaughter hygiene remain imperative for effective risk management to protect consumers in a sustainable One Health approach. [ABSTRACT FROM AUTHOR]