Assessment of Diversity of Antimicrobial Resistance Phenotypes and Genotypes of Mannheimia haemolytica Isolates From Bovine Nasopharyngeal Swabs

• Published in: Frontiers in veterinary science Vol. 9; p. 883389
• Main Authors: Carter, Hannah F, Wills, Robert W, Scott, Matthew A, Thompson, Alexis C, Singer, Randall S, Loy, John Dustin, Karisch, Brandi B, Epperson, William B, Woolums, Amelia R
• Format: Journal Article
• Language: English
• Published: Switzerland Frontiers Media S.A 11-05-2022
• Subjects: bacteria; cattle; pasteurellaceae; resistance; respiratory; Veterinary Science; cattle; bacteria; respiratory; pasteurellaceae; resistance
• ISSN: 2297-1769; 2297-1769
• DOI: 10.3389/fvets.2022.883389

The threat of bovine respiratory disease (BRD) for cattle operations is exacerbated by increasing prevalence of antimicrobial resistance (AMR) in
, a leading cause of BRD. Characterization of AMR in
by culture and susceptibility testing is complicated by uncertainty regarding the number of colonies that must be selected to accurately characterize AMR phenotypes (antibiograms) and genotypes in a culture. The study objective was to assess phenotypic and genotypic diversity of
isolates on nasopharyngeal swabs (NPS) from 28 cattle at risk for BRD or with BRD. NPS were swabbed onto five consecutive blood agar plates; after incubation up to 20
colonies were selected per plate (up to 100 colonies per NPS). Phenotype was determined by measuring minimum inhibitory concentrations (MIC) for 11 antimicrobials and classifying isolates as resistant or not. Genotype was indirectly determined by matrix-assisted laser desorption/ionization time of flight mass spectroscopy (MALDI-TOF MS). NPS from 11 of 28 cattle yielded at least one
isolate; median (range) of isolates per NPS was 48 (1-94). NPS from seven cattle yielded one phenotype, 3 NPS yielded two, and 1 NPS yielded three; however, within a sample all phenotypic differences were due to only one MIC dilution. On each NPS all
isolated were the same genotype; genotype 1 was isolated from three NPS and genotype two was isolated from eight. Diversity of
on bovine NPS was limited, suggesting that selection of few colonies might adequately identify relevant phenotypes and genotypes.