June 5, 2007 Some samples of the pathogen Campylobacter coli showed resistance to antibiotics that were intended to protect swine from diseases, tests performed at Iowa State University revealed. There’s more to be learned about the situation, which is keeping Qijing Zhang’s research team busy this year.
The project is a collaborative effort between Zhang, an ISU associate professor of veterinary microbiology, and Irene Wesley, a research microbiologist at the National Animal Disease Center in Ames, Iowa.
Zhang and Wesley are pursuing the research for the Food Safety Consortium. The matter of antibiotic resistance is a major one in scientific research these days. Zhang said although Campylobacter coli itself isn’t the main food safety concern, it could serve as reservoir of resistance for C. jejuni, a major foodborne pathogen in the U.S. and other countries.
“In terms of foodborne diseases in humans, Campylobacter jejuni is the predominant species,” Zhang said. “Campylobacter coli causes some problems, but not as significant as Campylobacter jejuni. Also, pork meat is not a main source of human Campylobacter infection.”
So, the reason for concern is that Campylobacter in swine can be transmitted to other farm animals, where greater potential for infection of humans can begin.
“Antibiotic resistance in swine is relevant to food safety, but in a different way,” Zhang explained. “It’s not like Campylobacter in poultry that can contaminate a bird or carcass.”
Zhang’s early results showed that Campylobacter coli was not resistant to the antibiotic ciprofloxacin (a fluoroquinolone), but he noted that was likely because ciprofloxacin is not used in U.S. swine production. Tests also showed that 56 percent of the Campylobacter coli isolates were resistant to the antibiotic doxycycline and 39 percent were resistant to erythromycin, another antibiotic. Fluoroquinolones and erythromycin are used in treating human Campylobacter infections.
“That’s why we need to put a lot of attention on ciprofloxacin and erythromycin,” Zhang said, “because these two classes of antibiotics are key weapons for treatment of people with Campylobacter infections.”
As the swine grow up and work their way through the production process, it might be expected that rates of resistance to antibiotics would increase along the way. But Zhang’s research didn’t show that on the one farm that had been researched. More farms are to be examined at which different stages of the production process will continue to be monitored. He wonders if the antibiotic resistance shows up randomly or if it increases over time.
“We’d assume that when you put the pigs in the nursery and eventually the finishing stages, they will probably get more exposed with antibiotics and that selection procedure would promote more resistance,” he said. “But so far we have not seen a progressive increase. That’s something we’re trying to figure out to see if it happens all the time or if it happened just on this farm.”
Zhang also seeks to determine if there is a correlation between antibiotic usage rates and resistance to antibiotics. The research hasn’t verified that yet among the swine.
Zhang’s long-term goal, through studying the ecology of antibiotic resistance, is to develop practical management measures that might help farmers reduce pathogens’ resistance to antibiotics.
“We’re going to get some science-based data and hopefully that can be used for design of intervention strategies or modifying practices in the future,” he said. “At this point we still have lots of questions to be answered. We’re also trying to develop a rapid testing technique to detect antibiotic-resistant pathogens not only in life animals but in processed meat.”
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