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

Abstract

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.

Keywords: E. coli; ESBL; MDR; colistin; meat lamb; sheep.

Figure 1

Timeline of in vivo and ex vivo sampling of meat lamb batches with an interval of at least three weeks. An additional in vivo sampling was necessary in 2020 due to slaughter scheduling for market demands.

Figure 2

Sampled areas on meat lamb carcasses. The carcass of each lamb was sampled using two swabs: one for the three outer zones (E1–E3), the other for the two internal zones of the two half-carcasses (I1–I2). The surface and areas were determined in accordance with Regulation (EC) n° 2073/2005 [14].