Researchers examine animal antibiotic resistance, possible human link

Feb 20 2008

It's bad enough when pathogenic bacteria work their way into the animal food supply.

Here's a related problem that has recently attracted scientists' attention: some of the pathogens may become resistant to the antimicrobials that are used to fight animal disease, and that might lead to more human resistance to the benefits of antibiotics.

“We're speculating that there may be a possibility of a link,” said Daniel Fung, a food science professor at Kansas State University who led research into the question for the Food Safety Consortium. “We are looking at it from the food scientist's standpoint. The resistant cultures may get into the food supply and may get into human beings. But those are speculations only.”

The work was done by Maggie Hanfelt and Mindi Russell under the direction of Fung and KSU College of Veterinary Medicine professionals.

Fung's research group targeted lagoons in Midwestern cattle feedlots because of concern over antimicrobial-resistant microbes being transferred into the food supply through water sources. In the feedlots, Fung explained, antimicrobials are used to treat sick food-producing animals such as cattle, poultry and swine.
Antimicrobials are also used to prevent disease and to promote growth.

The drawback, Fung said, is that the use of antibiotics as growth promoters appears to create large reservoirs of resistance to antibiotics in animals. That resistance could be transferred to humans who consume the food from those animals.

The KSU group looked at two types of feedlots: natural feedlots, which don't use antimicrobials in the cattle, and commercial feedlots, which use the antibiotics. Tests in the feedlots' lagoon water were conducted to measure the presence of E. coli and Enterobacter. The results consistently showed that the pathogens were more prevalent in the feedlot lagoons where the antibiotics were used.

Fung emphasized that the study is a preliminary one that raises questions. Veterinary medicine researchers are also interested in the situation and are starting to study gene pools and to track the resistant genes in the environment.

The studies of the lagoons showed that although those feedlots using antibiotics had higher rates of resistance to pathogenic bacteria, the natural feedlots still recorded instances of resistance. That's not unexpected, Fung said.

“That may be because of the naturally resistant organisms already in the environment anyway,” Fung said. “They would have some antibiotic resistance because of the organisms around the environment.”

Because antibiotics are used in the commercial feedlots, Fung said, it is reasonable to conclude that they would have more antibiotic-resistant cultures than the natural feedlots. But natural feedlots also use antibiotics when animals become ill.

“The vet school will do a lot more on this subject,” Fung said. “If we find out something really interesting that can relate to food safety directly, then we'll do some more work.

In any case, it's still important to find the answers because of the implications for antibiotic resistance in humans, Fung said.

“If humans receive antimicrobial cultures in their system and if they're sick from something, then the antibiotics will not be able to treat human beings. There are many antimicrobials in cultures in hospitals and places like that. And there aren't too many antibiotics discovered in the past 20 years.”