Those pesky house flies buzzing around your home or invading your springtime picnic could be doing more harm to human health than you realize. According to a recent study by Kansas State University, published in the Applied and Environmental Microbiology journal, insects carry antibiotic-resistant bacteria from one point to another, including from food animal farms and wastewater treatment facilities, for example, to urban areas.
“There are a number of insects that are commonly associated with animals, such as house flies and cockroaches,” said Ludek Zurek, K-State professor of microbial ecology and lead author on the published study. “House flies are common where animal manure is produced, including in cattle, poultry and swine operations. Cockroaches, primarily German cockroaches, have become a common pest in confined swine operations.”
Zurek and his colleagues collected house flies and cockroaches from food animal production locations, including swine and poultry farms, as well as wastewater treatment facilities that collect waste from multiple sources, including hospitals. The researchers then genetically analyzed the bacteria in the digestive tract of the insects and compared them to the bacteria present in the animal feces and wastewater.
“We found these insects carry the same bacteria found in the animal manure,” Zurek said. “Then we started sampling insects found in surrounding urban areas, including fast food restaurants, and again, we found house flies with multi-drug resistant bacteria.”
The house flies collected from the wastewater treatment plants, likewise, carried the same bacteria found in the waste itself, he said. House flies collected several miles from the wastewater treatment plants in surrounding urban areas had a lower prevalence of the antibiotic-resistant bacteria than those examined from the facilities themselves, but the bacteria still existed in those urban house flies.
The study led the researchers to conclude that insects, primarily house flies, can pick up antibiotic-resistant bacteria and disseminate them to surrounding areas. How serious that link is still needs to be investigated, but the potential is clearly there, Zurek said.
“Cockroaches and house flies are highly mobile, and they are attracted to residential areas,” he said. “They are attracted to our food and drinks. They have great potential to move multi-drug resistant bacteria to urban areas.”
In addition, Zurek’s team showed that bacteria in the house fly digestive tract can exchange antibiotic resistance by horizontal gene transfer. The resistant strains multiply in the fly and can be left behind on food by fly regurgitation or spitting, and defecation.