Brett Smith for redOrbit.com – Your Universe Online
Overuse of antibiotics in American agriculture and food production has long been a public concern over the potential for engendering more resilient microbes. A new study from Yale University shows that beneficial bacteria living in the gut of honeybees are demonstrating signs of resistance to such antibiotics.
A genetic analysis of the digestive bacteria showed eight different resistance genes for the antibiotic tetracycline in samples taken from U.S. honeybees, according to the research team´s report in mBio, the open-access journal for the American Society for Microbiology.
“It [resistance] seems to be everywhere in the U.S.,” said senior author Nancy Moran, from the Department of Ecology and Evolutionary Biology at Yale. “There’s a pattern here, where the U.S. has these genes and the others don’t.”
Honeybees have been given doses of the antibiotic oxytetracycline over the past 60 years to guard against “foulbrood,” a bacterial epidemic that can wipe out a hive before beekeepers can take action. Many of the genes that convey the resistance to oxytetracycline also convey resistance for tetracycline, a common broad-spectrum antibiotic that was historically used to treat cholera.
Using a metagenomic analysis, the Yale biologists screened honeybees from several locations across the United States and also from Switzerland, the Czech Republic and New Zealand. The team also took samples from wild bumblebees from the Czech Republic.
They found that American honeybees´ microbiota has a more abundant and diverse set of tetracycline resistance genes than those from other countries, which have banned the use of the drug by beekeepers on their hives. However, the researchers noted that the genes were less prevalent in U.S. colonies that had not been exposed to the antibiotic for 25 years.
Moran said that the bacteria responsible for foulbrood have also been found to be resistant to the antibiotics. Since oxytetracycline is a broad-spectrum antibiotic, it was likely capable of selecting for resistant genes in a wide range of bacteria.
“They carry tetL, which is one of the eight resistance genes we found,” she said. “It’s possible that the gene was transferred either from the gut bacteria to the pathogen or from the pathogen to the gut bacteria.”
The authors of the study point out the irony of fostering resistance and altering the bacteria that live in honeybee guts. In attempting to wipe out or prevent foulbrood, the decades of antibiotic doses may have actually been detrimental to honeybees´ overall health, which includes their microbiota.
Previous studies have suggested that these gut bacteria benefit the bees by neutralizing toxins in their diet, supplementing their nutrition, and defending them against pathogens. Therefore, a strategy designed to protect the bees from harm may actually have weakened their ability to fight off other pathogens.
Moran pointed out that the study could have implications for how honeybee diseases are prevented or treated; the antibiotic-resistance genes in the honeybee gut bacteria doesn’t pose a direct risk to humans. These microbes “don’t actually live in the honey, they live in the bee,” Moran said.
“We’ve never actually detected them in the honey. When people are eating honey, they’re not eating these bacteria.”
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