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Landmark antimicrobial study should redirect resistance hunt

I don’t know about Canada’s consumer and government agency attitudes, but down here in the States, steam has been building for decades to take antibiotics away from livestock producers, mainly because of resistance problems in the human population. There wasn’t any evidence that some sort of resistance could be passed from animal to human in meat products. But better-safe-than-sorry attitudes have been gaining ground. Those attitudes have fostered the “no antibiotics” meat products, the extremes of which have practically implied there was someone on the meat-processing line injecting antibiotics in meat cuts.

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Even if your bureaucrats and medical establishment authority figures are more enlightened than ours down here, you all have the problem of shipping cattle or meat down here that meets U.S. standards.

So there was joy when I read a recent study. And, while we’re proud of the folks involved down here, Canadians can also be proud of your share in this triumph.

This study was to use advanced genomic sequencing technology to identify genes that carried antibiotic resistance factors, track them through feedlot cattle and their environment, from feedlot entry to end products at the packing house and see if those resistance factors were passed along through meat or the environment.

The study involved 16 researchers from Colorado State University; Agriculture and Agri-Food Canada Lethbridge Research Centre; University of Saskatoon and the University of Colorado, Denver School of Medicine.

The study pooled samples from eight different pens of cattle totalling 1,741 head, in four different feedlots in Colorado and Texas. Any antimicrobial drug administration was documented and the researchers tracked antimicrobial resistance genes at key points along the feeding and processing trail. Interestingly, at the genomic level, they identified over 300 unique antimicrobial resistance genes. But during the feeding period, the array of antimicrobial resistance genes narrowed, indicating there were selective pressures in the feedlot.

The really good news came after processing. Did all the interventions packers now use during processing to drastically reduce pathogen incidence affect the resistance genes? Testing the beef trimmings after processing, the researchers found no antimicrobial resistance genes. In cautious research language, that “suggests” that the processing interventions eliminate the antimicrobial resistance genes that could be transmitted to humans and suggests beef products are not a likely source of antimicrobial resistance.

Noelle R. Noyes, clinical sciences, Colorado State University, and the team used next-generation sequencing to describe the antibiotic resistance potential (known as the “resistome”) found in a sample, whether taken from feed yards, trucks or packing plants. The team followed the resistome population, discovering that some groups of resistance genes at the beginning of the feeding period disappeared by its end. Most of the resistance groups that remained for the entire period correlated with whatever antibiotics were used in these cattle. But when the resulting beef products were sampled, no resistance groups could be found.

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 researchers collected pooled samples of manure, soil and water in pens at multiple points before and after the feeding period, from transport trucks, packing house holding pens, and after processing, of the carcass-cut conveyor belt and from trimmings.

The cattle were fed typical corn-based rations and handled normally as to animal health and doctoring but by pen riders who were unaware of the study. 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.

Researchers found some interesting environmental discoveries. A small number of soil and water samples, involving a feed yard 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.

“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 enabled by 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 U.S. National Beef Checkoff.

Question is, will the first example of solid science stop speculative government policy assuming that antibiotic resistance is significantly related to livestock antibiotic use? Thanks to U.S. and Canadian researchers and the American beef checkoff we have an astounding first shot.

The full text of this study was published in the peer-reviewed scientific journal eLife at elifesciences.org, March 8, 2016, under the title, “Resistome diversity in cattle and the environment decreases during beef production.”

About the author

Contributor

Steve Dittmer is the CEO of Agribusiness Freedom Foundation, a non-profit group promoting free market principles throughout the food chain. He can be reached at [email protected]

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