Use of REP‐PCR and 16S rRNA gene sequencing for comparison of Mannheimia haemolytica isolates obtained from fatal cases of bovine respiratory disease in the USA and Australia

OBJECTIVE: Assess the variability of Mannheimia haemolytica isolates obtained from fatal cases of bovine respiratory disease (BRD) in the USA and Australia using repetitive sequence‐based PCR (REP‐PCR) and sequencing of the 16S ribosomal RNA (rRNA) gene. METHODS: We examined 22 isolates from the USA and 36 isolates from Australia using (GTG)₅ and BOX‐A1R REP‐PCR primers, as well as sequencing a 700‐base pair length of the 16S rRNA gene. The discriminatory ability of each typing method was assessed and correlation coefficients were calculated to assess concordance between the results of each approach. RESULTS: All methods appeared to discriminate among isolates, with BOX‐A1R being the most sensitive and sequencing the least sensitive. Modest to moderate diversity was seen among the isolates, with as much variation within a continent as between the two. CONCLUSIONS: Using samples from diverse origins may permit extrapolation even to isolates with distant geographic and temporal relationships. Further, this information can serve as a baseline in assessing whether M. haemolytica is an opportunistic pathogen or if there are notable features that distinguish commensal isolates from those more likely to be associated with disease.