|WOOLUMS, AMELIA - MISSISSIPPI STATE UNIVERSITY|
|KARISCH, BRANDI - MISSISSIPPI STATE UNIVERSITY|
|EPPERSON, WILLIAM - MISSISSIPPI STATE UNIVERSITY|
|SMITH, DAVID - MISSISSIPPI STATE UNIVERSITY|
|BLANTON, JOHN - MISSISSIPPI STATE UNIVERSITY|
|AUSTIN, FRANK - MISSISSIPPI STATE UNIVERSITY|
|KAPLAN, RAY - MISSISSIPPI STATE UNIVERSITY|
|GUPTA, SUSHIM - ORISE FELLOW|
|MCCLELLAND, MICHAEL - UNIVERSITY OF CALIFORNIA|
Submitted to: Veterinary Microbiology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/7/2018
Publication Date: 6/8/2018
Citation: Woolums, A., Karisch, B., Frye, J.G., Epperson, W., Smith, D., Blanton, J., Austin, F., Kaplan, R., Hiott, L.M., Woodley, T.A., Gupta, S., Jackson, C.R., McClelland, M. 2018. Multidrug resistant Mannheimia haemolytica isolated from high-risk beef stocker cattle after antimicrobial metaphylaxis and treatment for bovine respiratory disease. Veterinary Microbiology. 221:143-152. https://doi.org/10.1016/j.vetmic.2018.06.005.
Interpretive Summary: Between cow-calf farms, where calves are borne and reared, and the feed lots used to finish beef cattle, calves go through stocker farms. Stocker farms purchase calves at auction and collect them into large groups ready for sale to feed lots. Stocker calves are especially prone to bovine respirator disease (BRD) due to stresses including weaning and transport. Herds are often treated with antibiotics to prevent BRD, a practice called metaphylaxis. Recently the bacteria that cause BRD have been reported to be multi-drug resistant or MDR, which are resistant to > 3 classes of antibiotics. To describe the prevalence of MDR bacteria in BRD, 50 stocker cattle were studied over a 21 day period from arrival on the farm. The cattle received tildipirosin metaphylaxis on day 0 and were also treated with up to 3 additional AM if they developed BRD; including: florfenicol, ceftiofur, and enrofloxacin. Nasopharyngeal swabs were collected on days 0, 7, 14, and 21, and cultured for bacteria that cause BRD. Mannheimia haemolytica was isolated from 4 of 48, 27 of 50, 44 of 50, and 40 of 50 cattle on days 0, 7, 14, and 21, respectively. One of 5, 27 of 27, 43 of 44, and 40 of 40 of these isolates were MDR on days 0, 7, 14, and 21, respectively. Twenty-four cattle required at least one BRD treatment, and MDR M. haemolytica was isolated from 13 of 24 treated cattle. One hundred-eighteen M. haemolytica isolates were genotyped and found to be highly diverse. Thirty-three isolates were analyzed by genome sequencing and up to 14 antibiotic resistance genes were detected in these isolates. This study indicates that MDR M. haemolytica is highly prevalent and genetically diverse in stocker cattle. This information is vital to understanding MDR bacteria causing BRD and developing methods to prevent it.
Technical Abstract: Antimicrobial resistance (AMR) in bacterial respiratory pathogens in high-risk stocker cattle has been poorly characterized. The objective of this study was to describe the prevalence of multidrug resistant (MDR; resistance to > 3 antimicrobial classes) respiratory pathogens in 50 conventionally managed stocker cattle over 21 days after arrival. Cattle received tildipirosin metaphylaxis on day 0 and were eligible to receive up to 3 additional antimicrobials for bovine respiratory disease (BRD): florfenicol, ceftiofur, and enrofloxacin. Nasopharyngeal swabs were collected on days 0, 7, 14, and 21 for bacterial culture and antimicrobial susceptibility testing using disc diffusion and broth microdilution. Mannheimia haemolytica was isolated from 5 of 48, 27 of 50, 44 of 50, and 40 of 50 cattle on days 0, 7, 14, and 21, respectively. One of 5, 27 of 27, 43 of 44, and 40 of 40 M. haemolytica were MDR on days 0, 7, 14, and 21, respectively. Pasteurella multocida was isolated from 6 of 48 cattle on day 0 and none were MDR; no other pathogens were isolated. Twenty-four cattle required at least one AM treatment; M. haemolytica was isolated from 13 of 24 treated cattle and all were MDR. One hundred-eighteen M. haemolytica isolates were subjected to pulsed-field gel electrophoresis (PFGE); multiple genotypes were identified. Whole genome sequencing of 33 isolates revealed 14 known AMR genes. Multidrug resistant M. haemolytica can be highly prevalent and genetically diverse in stocker cattle; additional research is necessary to determine factors that influence prevalence and the impact on cattle health.