Meat, Antibiotics and Superbugs: Is There A Connection?

Slaughtered meat found not to have drug-resistant bacteria, prompting calls for a new focus on environmental factors by Colorado State researchers

Researchers have found that humans -- and not meat -- might be the actual source of antibiotic-resistant illnesses.

Bacteria that do not respond to antibiotics infect about 2 million Americans each year, according to the Centers for Disease Control and Prevention (CDC). About 23,000 of those affected die from these antibiotic-resistant illnesses, or superbugs.

These illnesses are created when excessive antibiotic use kills bacteria the body needs. The body's good bacteria responds to antibiotics, while bad bacteria does not. When antibiotics are overused and good bacteria is killed, bad bacteria proliferates inside the body and cannot be killed off with treatment.

According to the CDC, not only is overuse of antibiotics to blame for superbugs, but so are antibiotics in meat, which the CDC says are transferred to humans.

However, after testing meat and fertilizer samples, scientists from Colorado State University have found that not only does meat not contain the genes for antibiotic resistance, but soil and feces inside cattle pens contain strains that could be traced back to humans and the environment. In other words, humans, their pets and the environment could be transferring antibiotic resistant genes to cattle - and then back again.

"Our findings clearly show that the spread of resistance is not a one-way street from animals to humans and that, as new evidence emerges, we need to shift focus," lead author Noelle Noyes, a postdoctoral fellow in the Department of Clinical Sciences at Colorado State University, said in a press release.

In this study funded by the Beef Checkoff, a marketing and research firm financed by meat producers, researchers examined about 1,700 cattle samples from throughout the production process. The authors found that antibiotic bacteria could be found in the feedlot, but not in the packaged meat.

"While we expected to find fewer bacteria and thus resistance genes, the absence of resistance genes in these samples was still a bit startling," co-principal investigator Paul Morley, a professor of clinical sciences at the university, said in the release.

The researchers said this absence could be because current measures to protect consumers--such as steam and cutting off potentially infected parts of carcasses--are effective in warding off bacteria like e.coli and salmonella.

"We need to expand our thinking in this area, and develop new and improved methods to better understand how antibiotic use drives a complex network of genetic modifications within entire microbial communities," co-principal investigator of the study, Keith Belk, a professor in the Department of Animal Sciences at the university, said in the release.

The researchers recommend that government bodies switch their focus to environmental factors when considering the growth of antibiotic-resistant bacteria. These factors could include wind currents, water flow and determining how far the bacteria can travel.

"The next challenge is to identify what is really driving the change we saw and to determine whether these drivers need to be modified and, if so, how," Noyes said in the release. "What concerns us most is ensuring that rational, science-driven discussion drives progress."

This study was published March 8 in the journal eLife.

This study was funded by the the Beef Checkoff.

No conflicts of interest were disclosed.