Antibiotic Resistance in Bovine Respiratory Disease Bacteria

Background

The Public Health Agency of Canada’s (PHAC) Canadian Integrated Program for Antimicrobial Resistance Surveillance (CIPARS) has conducted antibiotic resistance surveillance in cattle entering packing plants and retail beef since the mid 2000’s and began surveillance for antibiotic use and resistance in feedlot cattle in 2019. Because PHAC is focused on human health, it concentrates on antibiotic resistance in bacteria that are found in the intestinal tract of both livestock and humans (e.g. E. coli, Campylobacter, Enterococcus). But feedlots use antibiotics to combat pathogens like the respiratory bacteria involved in bovine respiratory disease (BRD). Understanding the prevalence of and trends in antibiotic resistance in BRD bacteria is critical to informing responsible antibiotic stewardship in feedlot animal health programs.

Objectives

The objectives of the CIPARS feedlot antibiotic use and resistance study are to:

• Provide representative estimates of antibiotic use and resistance in Canada’s finishing feedlot sector,
• Provide a unified approach to monitor trends in antibiotic use and resistance over time,
• Investigate associations between antibiotic use and resistance periodically (on a targeted basis) based on emerging resistance trends, and

• Provide collated industry data for the assessment of the potential public and animal health risk of antibiotic use in the Canadian finishing feedlot sector.

This specific project added information regarding antimicrobial sensitivity and resistance among Pasteurella multocida and Histophilus somni obtained from nasopharyngeal swabs of feedlot cattle at arrival and rehandling.

What they DID

The broader surveillance effort collected antibiotic use records submitted by veterinarians from participating feedlots in Alberta, Saskatchewan and Ontario. Fecal and nasopharyngeal samples were collected from finishing cattle in these same feedlots to identify organisms with relevance for human health (E. coli, Salmonella, Campylobacter and Enterococci) and BRD pathogens (Mannheimia haemolytica), respectively.

This funding expanded the overall project to include antibiotic susceptibility testing for two additional BRD pathogens (Pasteurella multocida and Histophilus somni) isolates collected at arrival and re-handling over the course of the three-year study.

Each year, deep guarded nasopharyngeal samples were collected from 16 cattle in each of 26 feedlots at entry and then again at rehandling. The same lot of cattle of cattle were sampled each time, though not necessarily the same individual animals. During sampling, cattle were restrained in the chute, had their nose wiped clean, and then had a swab inserted deep in the nasal cavity for collection according to a standard protocol. After collection, samples were packed and shipped to the laboratory for isolation of BRD pathogens M. haemolytica, P. multocida, and H. somni. Recovered isolates were tested for susceptibility to a panel of antibiotics using the broth microdilution method.

What They Learned

Over half of the recovered BRD isolates were susceptible to all tested antibiotics with established breakpoints. M. haemolytica and P. multiocida, were most commonly resistant to macrolide antibiotics (e.g., Zactran, Zuprevo, Micotil and Draxxin). H. somni was most commonly resistant to tetracycline, followed by resistance to macrolides. This was not surprising because macrolide and tetracycline antibiotics are routinely used to prevent and treat disease in feedlot cattle.

Resistance to fluoroquinolone antibiotics (e.g., A180 and Baytril) was detected in M. haemolytica and P. multocida. Fluoroquinolone and other Category I antibiotics are of very high importance in human medicine, and it will therefore be critical to monitor the trends in resistance to these antibiotics over time.

While changes were not always statistically significant, increases in resistance to select antibiotics between the arrival and re-handling time points were observed for both M. haemolytica and P. multocida. This finding is worth monitoring as increases in resistance over the feeding period may be due to pressure from AMU in the feedlot, spread of AMR within the feedlot, or both. If these trends continue over time, additional studies may be necessary to examine the drivers of resistance and the best strategies to mitigate further AMR development. In contrast, H. somni isolates had higher resistance to several antibiotics at feedlot arrival than at rehandling. This may indicate that the factors influencing AMR in H. somni are associated with earlier production phases. If this trend continues, there would be value in assessing cattle prior to arrival in the feedlot and investigating risk factors for their potential association with AMR

What it Means

Monitoring trends in AMR at both feedlot arrival and animal rehandling (i.e., after animal mixing and potential antibiotic exposure) is critical. This information is useful to feedlot veterinarians and their clients as they strive to reduce disease risk, improve treatment efficacy (reduce morbidity and mortality), support antibiotic stewardship, and improve feedlot production sustainability. Data from the surveillance system is critical to ensure that unrealistic and uneconomic production constraints that negatively impact animal health and welfare are not imposed on industry. This surveillance network underscores the beef industry’s social responsibility to the public while supporting science-based policy and regulation, economically sustainable beef production, trade, food security, and cattle health and welfare.