B.FLT.3011 - Bovine respiratory disease pathogen antimicrobial resistance surveillance and genetic sequencing

Summary

Bovine respiratory disease (BRD) is the most important infectious disease affecting feedlot cattle and the main indicator for therapeutic use of antimicrobials in the feedlot industry. BRD costs the Australian feedlot industry >$40 million annually. Initiated by a complex of viruses, secondary bacterial infection results in pneumonia causing high mortality if untreated. The main bacterial causes of BRD are Mannheimia haemolytica, Pasteurella multocida, Histophilus somni, Trueperella pyogenes and Mycoplasma bovis.

Internationally, antimicrobial resistance (AMR) has rapidly developed in BRD pathogens in North America due to the widespread dissemination of mobile genetic elements called integrative conjugative elements (ICEs) containing multiple resistance genes. In previous work (B.FLT.3004) in 2019 the first cases of AMR in P. multocida, the most prevalent BRD pathogen on Australian feedlots, was identified, with variable feedlot-dependent frequency of resistance to macrolides, tetracyclines as well as dual resistance.

For the first time in Australia, Mycoplasma bovis was shown to be a significant BRD pathogen, was often found co-associated with P. multocida, and emerging resistance to macrolides was observed. No antimicrobial resistance was observed in H. somni and a single macrolide-resistant M. haemolytica isolate was suggestive of a gene transfer event with P. multocida.

This project conducted bovine respiratory disease pathogen surveillance across a number of pilot feedlots in Queensland, New south wales, Victoria and South Australia during 2020 and 2021.

Objectives

(1) Conduct further pilot surveillance of antimicrobial resistance of bovine respiratory disease pathogens to train feedlots and veterinarians in this field.
(2) Characterise the genetic mechanisms responsible for recently identified resistance in Pasteurella multocida
(3) Complete whole of genome sequencing of Histophilus somni and Mycoplasma bovis collections for surveillance of antimicrobial resistance genes.

Key findings

• Newly described ST394 and globally significant ST79 were the predominant P. multocida sequence types causing BRD on Australian feedlots, with ST394 isolates more likely to carry antimicrobial resistance genes.
• Prevalence of resistance to macrolides, tetracyclines and dual resistance among P. multocida had increased to 48.8%, 30.2% and 27.9%, respectively, compared to 2019, but these results may have been impacted by the larger number of samples received from feedlots two feedlots where resistant strains are endemic.
• Additionally, several more macrolide-resistant M. haemolytica isolates were detected at different feedlots that did not take part in the 2019 study.
• Antimicrobial resistance was still negligible in H. somni and whole genome sequence analysis of the previous H. somni collection revealed that the isolates were genetically homogeneous.

Benefits to industry

MLA has supported pilot AMR surveillance of bovine respiratory disease pathogens from 2019 to 2021. This has upskilled feedlot managers and consulting veterinarians in the practice in collaboration with state veterinary diagnostic laboratories. By incorporating surveillance feedlots can support antimicrobial stewardship.

MLA action

MLA has presented the results of this research at the ALFA/MLA Consulting Veterinarian and Nutritionist meeting.

Future research

A number of pathogen strains have been identified for future research on vaccine development, to prevent and lower antimicrobial use.

Feedlots are now equipped to conduct their own internal surveillance in consultation with their prescribing veterinarian.