Antibiotic-resistant genes found in environment but not in food
Environmental pathways might pose a greater risk than the food supply for the transfer of antibiotic-resistant infections to humans, suggests a recent study by US and Canadian researchers.
The study was conducted with cattle, but its findings are still relevant to the poultry industry.
The investigators pooled samples from over 1,700 cattle in eight different pens in four different feedlots in two different states. They collected soil, water and manure samples in multiple stages, from incoming feeder cattle through post-slaughter, and using the latest DNA sequencing technology, identified over 300 unique antimicrobial resistance genes, reports meatpoultry.com
During the feeding period, however, the array of antimicrobial resistance genes narrowed, indicating selective pressures. All cattle had received macrolides (tylosin) in the feed, but administration of antimicrobial drugs to individual animals was infrequent; at least one animal within each group received doses of tetracyclines.
When the researchers tested beef trimmings during processing — perhaps the most likely place for contamination to occur — the researchers found no antimicrobial resistance genes.
This suggests the interventions packers use today for pathogens appear to remove the antimicrobial resistance genes that could be transmitted to humans and suggests that beef products are not a likely source of antimicrobial resistance.
Upon environmental testing, the researchers made a notable discovery. A very small number of soil and water samples from a feedyard pen, a plant holding pen and trucks showed the presence of resistance genes to antibiotics not used in cattle. It is unclear whether these antimicrobial resistance genes were triggered by the use of other drugs or migrated there via feedlot workers, working dogs or horses, or through air or water.
The results suggest that slaughter-based intervention systems minimize the likelihood of antimicrobial resistance genes being passed through the food chain and highlight the potential risk posed by indirect environmental exposures, conclude the researchers, from Colorado State University, the University of Colorado Denver School of Medicine and the Agriculture and Agri-Food Canada Research Center.
“While our results are more directly relevant to large North American feedlot operations, the general approach can easily be extended to other sectors of beef production, other countries and other livestock production systems,” they say in their published report on elifesciences.org.