By Rita Brhel

Antibiotic resistance is a hot topic among consumers right now, and the beef industry gets a fair share of the blame. But the problem is a lot bigger than livestock antibiotic use.
The development of antimicrobial resistance is a worldwide problem, including regions far beyond conventional beef production.
“Most of our antibiotics we use today were developed from soil bacteria, and antibiotic resistance began there,” said Terrance Arthur, microbiologist at the U.S. Meat Animal Research Center (MARC) near Clay Center, Neb.
“Any place there’s bacteria, there’s going to be resistance,” added John Schmidt, MARC microbiologist.
Select scientists shared their research during a Beef Research Update on April 25 at MARC. Arthur and Schmidt are part of the Meat Safety and Quality Research Unit, a leading team of researchers working to address the public’s concerns of antimicrobial resistance.
Arthur shared a study sorting out whether the issue of antimicrobial resistance is more of a matter of selection, as in antibiotic use, or rather a matter of enrichment in the microbial environment.
The first part of the study was to compare levels of antibiotic-resistant bacteria in the manure of conventionally raised cattle and cattle raised entirely without antibiotics. The data found very little difference between the two production types, but a noticeable difference in microbe levels per season, Arthur explained. Resistant bacteria levels were low in winter and high in summer.
“The more important thing is, we saw this resistance in untreated areas,” Arthur said.
This finding led to a comparison study of grass lawn never having exposure to livestock or manure. After adding water, Arthur’s team found the same seasonal results in resistant microbe levels on the lawn as in the cattle pens. Surprisingly, the levels of resistant bacteria were even higher than found in manure.
“We’re looking at a very serious antibiotic resistance issue just in the soil,” Arthur said.
These results appear to point toward environment, versus antibiotic use, as more related to resistant bacteria numbers.
While this research reveals that it is not just antibiotic use that contributes to an antibiotic-resistant microbial environment, it does not entirely rule out conventional beef production systems as a possible contributor. To investigate this, MARC microbiologist Jim Wells compared samples from the pen floors of both cattle raised without antibiotics and conventionally raised cattle that had been treated with an antibiotic for a respiratory condition caused by resistant bacteria.
The results mirrored Arthur’s findings with healthy conventional cattle. In both the manure and pen surface, bacterial counts varied by diet and season rather than by production system.
A follow-up study is currently looking into how long antibiotic-resistant bacteria remain in empty pens. A possible future study could measure if pen-cleaning affects bacteria numbers.
When it comes to testing for antibiotic-resistant bacteria, it is not a question of whether the microbes will be found but how many. This rule also applies for meat.
Not all bacteria are equal, however. There are bacteria that pose no threat to humans, and there are antibiotic-resistant bacteria that are of concern.
“Each and every one of us harbors these resistant strains,” Schmidt said. “There’ve been studies on that.”
But until Schmidt’s study on differences in levels of resistant microbes in meat from cattle raised without antibiotics and meat from conventionally raised cattle, there had not been any beef-specific evidence of this. It did not come as a surprise that there were no differences in resistant bacteria counts on the meat of cattle from either production system.
“Microbiomes differ more by supplier than by production system,” he said.
The leading theory is the packaging is a dominant influencer in varying levels of bacterial counts in meat, but Schmidt admitted that the research is lacking to back this up. MARC is beginning to explore this, however, as microbiologist Rong Wang, has been looking at improving processing interventions. In one of his studies, he found that antibiotic-resistant E. coli and Salmonella team up to create a microbial layer on meat that is more resistant to removal by current sanitizers than by either bacterial species on its own. Future studies will determine if different sanitizers would be more effective in removing these biofilms.
All in all, there is good news. Through each of these studies, MARC scientists are demonstrating that antibiotic use typical to conventional beef production systems does not result in increased antibiotic-resistant bacteria in either cattle or meat products, Schmidt said. While overall antimicrobial resistance is a growing issue around the world, antibiotic use in the beef industry is not a major contributor.