In the last edition, we outlined the context and the basics of a study that used new advanced genetic sequencing techniques to identify antimicrobial resistance genes and then trace them through a feeding and processing cycle. The critical finding was that interventions during packing house processing eliminated the antimicrobial resistance genes so that they were not present in finished beef products. That means that speculation that antimicrobial resistance could be passed on to humans through beef products looks highly unlikely, at least from this first, thorough study.

This Noyes study is the first to "have specifically tracked antimicrobial use in cattle while investigating antimicrobial resistance in market-ready products or consumers." The Meat+Poultry story noted.

In other words, this study is meant to provide clinical evidence in an area of important public policy that has been characterized by possible theories, no hard evidence but a "better safe than sorry" approach by some public officials.

This study tracked two pens of cattle in each of four feedyards (eight cohorts, 1,741 total head) in two states, Colorado and Texas. The researchers collected pooled samples of manure, soil and water in those pens both when the cattle arrived and when they were ready for slaughter. Samples were taken from the inside walls of the trucks transporting cattle to the packing house after unloading, again while cattle were in the holding pen at the packing house and, after slaughter and processing, of the conveyor belts moving carcass cuts and from trimmings used to make ground beef from these animals.

The cattle were fed typical corn-based rations and handled as to animal health and doctoring as is typical but by pen riders who were unaware of the study. Days on feed ranged from 117 to 227 correlated to incoming weights. All cattle received macrolides (tylosin) in the feed but administration of antimicrobial drugs to individual animals was infrequent. However, at least one animal within each group received doses of tetracyclines.

"At the packing plant, typical antimicrobial interventions were used during carcass processing, including hot water pasteurization, lactic and peroxyacetic acid spray, as well as knife trimming and spot steam vacuuming," the Meat+Poultry story noted.

While no antimicrobial resistance genes were found in the meat trimming samples at the processing plant, researchers found at least one class of antimicrobials that didn't conform to the pattern of its antimicrobial resistance genes disappearing in the feedyard phase if the animals were not exposed to the antimicrobial. The aminoglycoside class of antimicrobial resistance genes remained prevalent even though those drugs were not used. This suggests the relationship between drug use and antimicrobial resistance is not straightforward.

"Researchers found some interesting environmental discoveries. A small number of soil and water samples, involving a feedyard pen, a plant holding pen and trucks, showed the presence of antimicrobial resistance genes that were not used on the study cattle, are not cleared for cattle but confer resistance to antimicrobials important in human health. 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," Meat+Poultry said.

"While our results suggest that slaughter-based intervention systems minimize the likelihood of intact antimicrobial resistance genes being passed through the food chain, they also highlight the potential risk posed by indirect environmental exposures to the feedlot resistome," the study concluded.

This study was conducted through the support of JBS USA packing plants, Fiver Rivers Cattle Feeding, and the University of Colorado Denver High Throughput Sequencing Core, which is supported in part by the Genomics and Microarray Shared Resource of Colorado's NIH/NCI Cancer Center Support Grant. It was funded by the National Beef Checkoff.

So this checkoff-funded study should certainly put the brakes on speculative government policy assuming that antibiotic resistance is significantly related to livestock antibiotic use but it opens lots of avenues for further research to learn how those and other factors interact to affect the resistance puzzle we have.

*Forsberg et al. 2012, Rolain, 2013

** "Antibiotic Resistance from the Farm to the Table," 2014

The full text of this study was published in the peer reviewed scientific journal "eLife" March 8, 2016, under the title, "Resistome diversity in cattle and the environment decreases during beef production." Click here to go to study text.