Antimicrobial Susceptibility and Resistance Mechanisms in Mannheimia haemolytica Isolates from Sheep at Slaughter
Investigation published in Animals
June 14th, 2023
Mannheimia haemolytica is a key bacterial pathogen contributing to important ruminant diseases and accounting for a large proportion of overall antimicrobial use in cattle and sheep. The recent emergence of ovine strains with reduced susceptibility to antimicrobials—which could lead to treatment failure, increased costs of livestock production, and the dissemination of antimicrobial-resistant genes to other bacteria and possibly the environment—is of concern. This study investigated the levels of antimicrobial resistance of M. haemolytica isolated from clinically healthy sheep at slaughter and the genetic bacterial resistance mechanisms. Low levels of phenotypic resistance were detected for most of the antimicrobials tested except for tetracycline (4.3%) and tylosin (89.1%). A few antimicrobial resistance determinants were found in the genome of six out of nine isolates, consisting of genes conferring resistance to tetracyclines (tetH), aminoglycosides (strA), and sulfonamides (sul2), which were sometimes linked to the presence of plasmids but did not always lead to resistance phenotypes. Our results suggest that there is limited resistance in M. haemolytica strains of veterinary origin, but the presence of several resistance genes, some of which were found in mobile genetic elements that play a major role in the dissemination of antimicrobial resistance in members of the Pasteurellaceae family, deserves further consideration
Alvarez J., Calderón-Bernal JM., Torre-Fuentes L., Hernandez M., Pinto-Jimenez CE., Dominguez L., Fernandez-Garayzabal JF., Vela AI. and Cid D.
 | Departamento de Sanidad Animal. Facultad de Veterinaria. Universidad Complutense (UCM). |
| Centro de Vigilancia Sanitaria Veterinaria (VISAVET). Universidad Complutense (UCM). |
 | Laboratorio de Biología Molecular y Microbiología. Instituto Tecnológico Agrario de Castilla y León (ITACyL). |
 | London School of Hygiene and Tropical Medicine (LSHTM). University College London (UCL). |
| Facultad de Medicina Veterinaria. Universidad Nacional Mayor de San Marcos. | |
