Researchers from Yale University have found resistance to the antibiotic tetracycline in U.S. honeybee gut bacteria, a discovery that could impact beekeeper efforts to keep hive-killing diseases at bay.

Photo: Louise Docker

In a study published this week in mBio, researchers found eight different tetracycline-resistant genes in honeybees that had been exposed to the medication.

Bees from countries where the antibiotic is banned did not experience the same resistance.

The findings could be the outcome of years of preventitive antibiotic use in domesticated U.S. hives. Oxytetracycline, an antibiotic that closely resembles tetracycline, has been used since the 1950s to treat a bacterial disease called "foulblood," which can wipe out hives more rapidly than beekeepers can fight it.

Many genes that cause resistance to oxytetracycline also cause resistance to tetracycline, the study said.

Nancy Moran, a senior author of the study, said resistance appeared to be widespread across the United States, in contrast to other countries observed.

Researchers screened for tetracycline-resistant genes in honeybees from the United States, and in three countries where oxytetracycline is prohibited: Switzerland, the Czech Republic and New Zealand. They found greater numbers of resistant bees and more diverse restistance in the United States.

"It seems likely this reflects a history of using oxytetracycline since the 1950s. It's not terribly surprising. It parallels findings in other domestic animals, like chickens and pigs," Moran said.

Moran noted that after years of oxytetracycline use, the foulbrood pathogens Melissococcus pluton and Paenibacillus larvae developed resistance to the tetracycline components of the antibiotic.

"They carry tetL, which is one of the eight resistance genes we found. It's possible that the gene was transferred either from the gut bacteria to the pathogen or from the pathogen to the gut bacteria," she said.

The study called for concern regarding antibiotic resistance, pointing out that decades of efforts to help bees may have actually been detrimental to their health.

According to the report, the bacterial residents of the honeybee gut help neutralize toxins in the bees' diet, improve nutrition and aid defense against pathogens. Longterm use could weaken resistance to other diseases.

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