Yale researchers have identified a potential culprit in a nationwide increase of honeybee deaths — resistance to an important antibiotic.

In the Oct. 30 issue of the mBio journal, Yale professor of ecology and evolutionary biology Nancy Moran published a study showing that beneficial bacteria found in the guts of honeybees have acquired genes that make bees resistant to tetracycline, an antibiotic used to prevent colony-destroying infections and other bacterial diseases. Moran’s research identified eight tetracycline-resistant genes in American honeybees that were absent in honeybee populations where such antibiotic treatment is banned, suggesting that use of tetracycline has genetically altered beneficial bacteria and made colonies more prone to infection.

“We noticed that the [first] colony collapses happened in 2006, which is when the antibiotic was first introduced,” Moran told the News. “But it’s really a very speculative concept right now.”

Researchers in Moran’s lab are looking to confirm the link they have established between antibiotics and colony collapses so as to impact policy-making in the beekeeping community.

“The beekeepers are interested in healthy bees. If we can show that antibiotics affect honey production or colony survival, we can draw their attention,” Moran said.

To test bee genes for resistance to antibiotics, researchers in Moran’s lab isolated all of the bacterial DNA in bee guts and transferred them into independent DNA molecules called plasmids. These plasmids were then put into E. coli and sequenced so that the tetracycline-resistant genes could be identified. To determine how different bee populations interact with antibiotics, researchers used a technique called polymerase chain reaction to amplify bee DNA samples collected from various locations in the United States, New Zealand, the Czech Republic and Switzerland.

“We found that bees from the USA, which had a long treatment history [with tetracycline], carried the most resistant genes,” said Waldan Kwong GRD ’16, one of the authors of the paper and a researcher in Moran’s lab.

If confirmed, Moran’s research could have wide-reaching impact on American crop growth and production. Honeybee pollination plays a critical role in the $15 billion U.S. agriculture industry. The industry has been plagued by recent bee colony collapses, due primarily to bees’ contraction of the bacterial disease foul brood.

University of California, Davis apiculture professor Norman Gary stressed the magnitude of the colony collapse disorder.

“Only recently has the true value of honeybees been appreciated by people in this country,” Gary told the News. “The colony collapse disorder is a complex issue and many scientists are advancing theories to explain its cause.”

Kwong said he hopes the research conducted in Moran’s lab will encourage beekeepers to exercise caution when introducing new antibiotics into bee colonies.

“Beekeepers and the general public should be aware that application of antibiotics not only affects pathogens but also the normal healthy microbes that coexist with the host,” he said. He added, however, that further research and consultation with the beekeeping community are needed before any new policies can be introduced and implemented.

Gary said bee die-offs are likely the result of multiple factors rather than a single central cause. “In the scientific community we’re hoping that honeybees will develop a resistance to the cause of the colony collapses,” he said.

Moving forward, researchers in Moran’s lab are studying the health benefits and hazards posed by gut bacteria in bees. They are studying the microbes that have become resistant to tetracycline to understand the beneficial functions they perform, such as pathogen defense, as well as the negative impact they can have on bees’ immune systems.

“We want to understand how bacteria function in bees,” Moran said. Her lab is currently working on an experiment that exposes bees to antibiotics and analyzes their long-term effects. Though she said the team has evidence that bacteria can help bees digest food, Moran said they hope to discover other health benefits bacteria provide bees.

“It’s basic work, but nothing like it has ever been done before,” she said.

The lead author of the paper was former Yale postdoctoral researcher Baoyu Tian, and other authors included Yale researchers Nibal H. Fadhil and J. Elijah Powell. The research was funded through a grant from the National Science Foundation.