Scientists have long known that waste beds of commercial chicken houses abound with potentially dangerous bacteria. But in April a team led by microbiologist Anne Summers of the University of Georgia reported that the beds are also littered with integrons, genes that can render those bacteria impervious to several antibiotics at once, making them nearly impossible to kill.
For 13 weeks, Summers and her colleagues sampled feces, skin, feathers, and other organic material from two major commercial chicken houses in Georgia. The scientists discovered high numbers of integrons not only in bacteria such as Escherichia coli and salmonella but also in germs that were previously assumed to be free of the resistance-forming genes, such as staphylococci. The result suggests that integrons are much more common, both in animals and the humans who handle them, than previously thought.
Microbiologists believe that integrons have existed for eons but took on their current role only after the development of the first antibiotics, which gave an advantage to microbes that could collect the resistance genes. These gene snippets spread when their bacterial hosts reproduce or acquire them from nearby dead cells. Moreover, integrons travel easily between humans, pets, livestock, and their wastes via bacteria that are inhaled or eaten. “We continually ingest bacteria from uncooked food, from our pets, from intimate behavior with other humans, and from putting our unwashed hands into our noses or mouths,” Summers says. “This is a warning bell.” It explains why antibiotic resistance spreads so quickly and extensively after drugs are introduced.