Antimicrobial resistance in fecal Escherichia coli and Salmonella enterica in dairy calves: a systematic review

Authors: SPRINGER, HAYLEY - Pennsylvania State University; DENAGAMAGE, THOMAS - Pennsylvania State University; FENTON, GINGER - Pennsylvania State University; Haley, Bradd; Van Kessel, Jo Ann; HOVINGH, ERNEST - Pennsylvania State University

Submitted to: Foodborne Pathogens and Disease
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/26/2018
Publication Date: 1/23/2019
Citation: Springer, H., Denagamage, T., Fenton, G., Haley, B.J., Van Kessel, J.S., Hovingh, E. 2019. Antimicrobial resistance in fecal Escherichia coli and Salmonella enterica in dairy calves: a systematic review. Foodborne Pathogens and Disease. 16:23-24. https://doi.org/10.1089/fpd.2018.2529.
DOI: https://doi.org/10.1089/fpd.2018.2529

Interpretive Summary: Antibiotic resistant bacteria remain a serious public health threat in the United States and abroad. Human infections with antibiotic resistant bacteria are often associated with human-to-human or environment-to-human transmission, while the role of food-producing animals in the transmission of these bacteria to humans is not as well-established. It is therefore important to further understand the role of food-producing animals as reservoirs of antibiotic resistant bacteria. In recent years, evidence has mounted that pre-weaning dairy calves (very young calves that are still being fed milk or milk replacer) harbor more antibiotic resistant microorganisms than do older, adult cows. To investigate the consistency of this observation and its possible relationships with how the animals are managed, we evaluated the scientific literature using a systematic approach. Data from previous studies were gathered from peer-reviewed research articles as well as student theses and dissertations. Data were included if these articles evaluated the presence of antibiotic resistant E. coli and/or Salmonella from pre-wean dairy calves in North America between 1997 and 2018. The research articles meeting these criteria were then further categorized into farm management practices and evaluated. Results of the systematic evaluation consistently support an association between pre-weaning calves and increased risk of shedding of resistant organisms. There was also evidence, though less consistent, of a role of antibiotic treatment, antibiotic-containing medicated milk replacer feeding, and nonsalable waste milk feeding on the presence of antibiotic resistant bacteria in the feces of pre-weaned dairy calves. Results of this systematic review indicate a need to further understand the physiological, ecological, and dairy calf management factors that influence the frequently observed high levels of antibiotic resistant bacteria in pre-weaned dairy calves. Such information may have the potential to identify intervention strategies to reduce the risk of transmission of antibiotic resistant pathogens between animals and from animals to humans.

Technical Abstract: There is consistent evidence that, compared to older animals, young dairy calves carry high levels of antimicrobial resistance (AMR) in fecal Escherichia coli and Salmonella enterica, providing a potential reservoir of AMR genes and foodborne or zoonotic pathogens. As veterinarians and dairy producers work together to develop practical and effective antibiotic stewardship policies for dairy calf rearing, it is vital to have a strong understanding of the current knowledge on antimicrobial resistance in this group of animals. We used a systematic review process to summarize the current evidence in the literature of associations between management practices and AMR patterns, as well as descriptive data on AMR in S. enterica and E. coli in dairy calves in North America. Seven online databases were searched for literature published from 1997 to 2018. Multiple studies indicate an association between pre-weaning calves and increased risk of shedding of resistant organisms. There was also evidence, though less consistent, of a role of antibiotic treatment, antibiotic-containing medicated milk replacer feeding, and nonsalable waste milk feeding on AMR organisms. Overall, our findings highlight the need for further research to improve our understanding of physiological and microbiological factors that may contribute to the high populations of resistant organisms in young calves, the impact of antibiotic exposure, through treatment, preventative, and dietary sources on resistant flora, as well as the role of non-antibiotic disease prevention practices in reducing antibiotic use and the impact of this on resistant organisms in young dairy calves.