Antimicrobial Resistance Genes in Respiratory Bacteria from Weaned Dairy Heifers
Sarah Depenbrock,
Cory Schlesener,
Sharif Aly,
Deniece Williams,
Wagdy ElAshmawy,
Gary McArthur,
Kristin Clothier,
John Wenz,
Heather Fritz,
Munashe Chigerwe,
Bart Weimer
Affiliations
Sarah Depenbrock
Department of Veterinary Medicine and Epidemiology, School of Veterinary Medicine, University of California Davis, Davis, CA 95616, USA
Cory Schlesener
Department of Population Health and Reproduction, 100K Pathogen Genome Project, School of Veterinary Medicine, University of California Davis, Davis, CA 95616, USA
Sharif Aly
Veterinary Medicine Teaching and Research Center, School of Veterinary Medicine, University of California Davis, Tulare, CA 93274, USA
Deniece Williams
Veterinary Medicine Teaching and Research Center, School of Veterinary Medicine, University of California Davis, Tulare, CA 93274, USA
Wagdy ElAshmawy
Veterinary Medicine Teaching and Research Center, School of Veterinary Medicine, University of California Davis, Tulare, CA 93274, USA
Gary McArthur
Swinging Udders Veterinarian Services, Galt, CA 95632, USA
Kristin Clothier
California Animal Health and Food Safety Laboratory, School of Veterinary Medicine, University of California Davis, Davis, CA 95616, USA
John Wenz
Field Disease Investigation Unit, Department of Veterinary Clinical Sciences, College of Veterinary Medicine, Washington State University, Pullman, WA 99163, USA
Heather Fritz
California Animal Health and Food Safety Laboratory, School of Veterinary Medicine, University of California Davis, Davis, CA 95616, USA
Munashe Chigerwe
Department of Veterinary Medicine and Epidemiology, School of Veterinary Medicine, University of California Davis, Davis, CA 95616, USA
Bart Weimer
Department of Population Health and Reproduction, 100K Pathogen Genome Project, School of Veterinary Medicine, University of California Davis, Davis, CA 95616, USA
Bovine respiratory disease (BRD) is the leading cause of mortality and antimicrobial drug (AMD) use in weaned dairy heifers. Limited information is available regarding antimicrobial resistance (AMR) in respiratory bacteria in this population. This study determined AMR gene presence in 326 respiratory isolates (Pasteurella multocida, Mannheimia haemolytica, and Histophilus somni) from weaned dairy heifers using whole genome sequencing. Concordance between AMR genotype and phenotype was determined. Twenty-six AMR genes for 8 broad classes of AMD were identified. The most prevalent, medically important AMD classes used in calf rearing, to which these genes predict AMR among study isolates were tetracycline (95%), aminoglycoside (94%), sulfonamide (94%), beta-lactam (77%), phenicol (50%), and macrolide (44%). The co-occurrence of AMR genes within an isolate was common; the largest cluster of gene co-occurrence encodes AMR to phenicol, macrolide, elfamycin, β-lactam (cephalosporin, penam cephamycin), aminoglycoside, tetracycline, and sulfonamide class AMD. Concordance between genotype and phenotype varied (Matthew’s Correlation Coefficient ranged from −0.57 to 1) by bacterial species, gene, and AMD tested, and was particularly poor for fluoroquinolones (no AMR genes detected) and ceftiofur (no phenotypic AMR classified while AMR genes present). These findings suggest a high genetic potential for AMR in weaned dairy heifers; preventing BRD and decreasing AMD reliance may be important in this population.
