Yale researchers found genetic evidence that helpful bacteria, which normally live the bellies of honeybees, have become highly resistant to the antibiotic tetracycline, possibly weakening the bees’ ability to fight disease.

Researchers say decades of use may have unknowingly encouraged antibiotic resistance by genetically altering the beneficial bacteria.

Past studies show helpful bacterial play an important role in protecting the honeybee by neutralizing toxins found in their diets while also helping fight off various pathogens.

The  researchers have identified eight different tetracycline resistance genes among U.S. honeybees that were exposed to antibiotics.  Those same resistance genes were missing in bees from countries where antibiotic use is banned.

“It seems to be everywhere in the U.S.,” says Nancy Moran of Yale University, a senior author on the study. “There’s a pattern here, where the U.S. has these genes and the others don’t.”

In the 1950s, beekeepers started using the antibiotic oxytetracycline, a compound similar to tetracycline, which is commonly used in humans. They were trying to fight a devastating bacterial disease called foulbrood, which can wipe out a hive more quickly than beekeepers can react to the infection.

But after years of use  the microorganisms eventually acquired a resistance to tetracycline, possibly weakening the honeybee’s resistance to other diseases.

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

The researchers took bee samples from the Czech Republic, New Zealand and Switzerland, which do not allow their beekeepers to use the antibiotics.

Researchers found  those bees had only two or three different resistance genes and even then only in very low numbers, suggesting that prolonged antibiotic use in the US bees may have played a role in developing the resistance genes.

Moran  points out that the antibiotic-resistant genes researchers found in the bellies of the honeybee do not pose a direct risk to humans.

Those microorganisms, according to Moran, “don’t actually live in the honey, they live in the bee. We’ve never actually detected them in the honey. When people are eating honey, they’re not eating these bacteria.”

Nancy Moran joins us this weekend on the radio edition of Science World.  She tells us more about how treatment meant to strengthen honeybee hives in the U.S. may have actually weakened them instead. Tune in (see right column for scheduled times) or check out the interview below.