Antimicrobial resistance in Mannheimia haemolytica from diseased cattle: phenotypic and genotypic insights over five years (2018-2022).
6 affiliations
- 1Oak Ridge Institute for Science and Education (ORISE), Animal and Plant Health Inspection Service (APHIS) Research Participation Program, Oak Ridge, TN, USA. [email protected].
- 2United States Department of Agriculture, Animal and Plant Health Inspection Service (APHIS), Veterinary Services, Diagnostics & Biologics, National Veterinary Services Laboratories (NVSL), National Animal Health Laboratory Network (NAHLN), Ames, IA, USA. [email protected].
- 3United States Department of Agriculture, Animal and Plant Health Inspection Service (APHIS), Veterinary Services, Diagnostics & Biologics, National Veterinary Services Laboratories (NVSL), Ames, IA, USA.
- 4United States Department of Agriculture, National Institute of Food and Agriculture (NIFA), Institute of Food Production and Sustainability, Kansas City, MO, USA.
- 5United States Department of Agriculture, Animal and Plant Health Inspection Service (APHIS), Veterinary Services, Diagnostics & Biologics, National Veterinary Services Laboratories (NVSL), National Animal Health Laboratory Network (NAHLN), Ames, IA, USA.
- 6United States Department of Agriculture, Animal and Plant Health Inspection Service (APHIS), Veterinary Services, Diagnostics & Biologics, National Veterinary Services Laboratories (NVSL), Ames, IA, USA. [email protected].
Abstract
Background
Mannheimia haemolytica is a gram-negative bacterium that typically resides in the upper respiratory tract of healthy cattle but can invade the lower respiratory tract in immunocompromised cattle, contributing to bovine respiratory disease (BRD). The rise of antimicrobial resistance (AMR) in M. haemolytica strains, especially those linked to BRD, is a growing concern. This study aimed to investigate AMR phenotypes and genotypes in M. haemolytica isolates collected during the NAHLN AMR Pilot Project (2018-2022) and assess the use of a previously developed single nucleotide polymorphism genotyping scheme to classify strains and identify associations between genotypes, AMR genes, quinolone point mutations (QPMs) and mobile genetic elements in diseased cattle.Results
Of 2743 isolates tested for antimicrobial susceptibility, 66.7% (1830/2743) were pan-susceptible, while 33.3% (913/2743) showed resistance to at least one antimicrobial, primarily tetracyclines. Among the 848 sequenced isolates, 36.7% (311/848) harbored AMR genes and/or QPMs. Of these, 59.8% (186/311) were phenotypically classified as multidrug-resistant; commonly detected AMR genes included aadA, ant(2'')-Ia, blaOXA-2, mph(E), msr(E), and tet(H). The study found that 88.3% (749/848) of isolates belonged to genotype 2, a group previously associated with BRD and AMR. Notably, 95.8% (298/311) of isolates harboring AMR genes were from genotype 2. Although most clinical isolates of M. haemolytica were pan-susceptible and lacked AMR genes, a substantial proportion of isolates exhibited AMR, with a high degree of concordance between genotype and phenotype across all antimicrobials tested. Most clinical isolates (749/848, 88.3%), primarily obtained from the cattle lungs rather than the upper respiratory tract, were classified as genotype 2. These isolates harbored a T4SS integrative and conjugative element (ICE, 283/848, 33.4%) as well as an integrative and mobilizable element (IME, 59/848, 7.0%) containing AMR genes.Conclusions
This study highlights a strong association between genotype 2 M. haemolytica and AMR, with a significant prevalence of multidrug-resistant strains. The findings underscore the importance of genotypic characterization and whole-genome sequencing (WGS) for monitoring AMR in M. haemolytica and informing future management strategies for BRD.
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BibTeX
@article{burciaga2026antimicrobial,
title = {{Antimicrobial resistance in Mannheimia haemolytica from diseased cattle: phenotypic and genotypic insights over five years (2018-2022).}},
author = {Selma Burciaga and Laura Alt and Kathe Bjork and Beth Harris and Christina Loiacono and Jessica Hicks},
journal = {BMC genomics},
year = {2026},
month = jul,
doi = {10.1186/s12864-026-12783-y},
url = {https://europepmc.org/article/MED/42958009},
note = {CC BY},
}
RIS
TY - JOUR
TI - Antimicrobial resistance in Mannheimia haemolytica from diseased cattle: phenotypic and genotypic insights over five years (2018-2022).
AU - Selma Burciaga
AU - Laura Alt
AU - Kathe Bjork
AU - Beth Harris
AU - Christina Loiacono
AU - Jessica Hicks
PY - 2026
DA - 2026/07/25
JO - BMC genomics
DO - 10.1186/s12864-026-12783-y
UR - https://europepmc.org/article/MED/42958009
AB - Background Mannheimia haemolytica is a gram-negative bacterium that typically resides in the upper respiratory tract of healthy cattle but can invade the lower respiratory tract in immunocompromised cattle, contributing to bovine respiratory disease (BRD). The rise of antimicrobial resistance (AMR) in M. haemolytica strains, especially those linked to BRD, is a growing concern. This study aimed to investigate AMR phenotypes and genotypes in M. haemolytica isolates collected during the NAHLN AMR Pilot Project (2018-2022) and assess the use of a previously developed single nucleotide polymorphism genotyping scheme to classify strains and identify associations between genotypes, AMR genes, quinolone point mutations (QPMs) and mobile genetic elements in diseased cattle.Results Of 2743 isolates tested for antimicrobial susceptibility, 66.7% (1830/2743) were pan-susceptible, while 33.3% (913/2743) showed resistance to at least one antimicrobial, primarily tetracyclines. Among the 848 sequenced isolates, 36.7% (311/848) harbored AMR genes and/or QPMs. Of these, 59.8% (186/311) were phenotypically classified as multidrug-resistant; commonly detected AMR genes included aadA, ant(2'')-Ia, blaOXA-2, mph(E), msr(E), and tet(H). The study found that 88.3% (749/848) of isolates belonged to genotype 2, a group previously associated with BRD and AMR. Notably, 95.8% (298/311) of isolates harboring AMR genes were from genotype 2. Although most clinical isolates of M. haemolytica were pan-susceptible and lacked AMR genes, a substantial proportion of isolates exhibited AMR, with a high degree of concordance between genotype and phenotype across all antimicrobials tested. Most clinical isolates (749/848, 88.3%), primarily obtained from the cattle lungs rather than the upper respiratory tract, were classified as genotype 2. These isolates harbored a T4SS integrative and conjugative element (ICE, 283/848, 33.4%) as well as an integrative and mobilizable element (IME, 59/848, 7.0%) containing AMR genes.Conclusions This study highlights a strong association between genotype 2 M. haemolytica and AMR, with a significant prevalence of multidrug-resistant strains. The findings underscore the importance of genotypic characterization and whole-genome sequencing (WGS) for monitoring AMR in M. haemolytica and informing future management strategies for BRD.
SN - 1471-2164
ER -