Honeybee Guts Carry Antibiotic Resistance Genes

Honeybees are prone to a bacterial disease "foulbrood".  It has been the scourge of beekeepers in the U.S. who have fought the infection, known to wipe out hives in a jiffy, with regular preventive applications of the antibiotic, oxytetracycline.Oxytetracycline is a compound that closely resembles tetracycline, which is commonly used in humans.

The antibiotic  has been in use among beekeepers since the 1950s, and many genes that confer resistance to oxytetracycline also confer resistance to tetracycline.

The latest study , conducted by researchers from Yale University, states that bacteria in the guts of honeybees are highly resistant to the antibiotic tetracycline. This could be because of decades of preventive antibiotic use in domesticated hives.

For the study they identified eight different tetracycline resistance genes among U.S. honeybees that were exposed to the antibiotic. During the research, they noticed that the genes were largely absent in bees from countries where such antibiotic use is banned.

"Resistance seems to be everywhere in the U.S.," said 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."

With the help of sensitive molecular techniques, Moran and her colleagues screened honeybees to check for the presence and abundance of tetracycline resistance genes. They screened honeybees from several locations in the U.S., Switzerland, the Czech Republic and New Zealand as well as several wild bumblebees from the Czech Republic.

The researchers noticed that U.S. honeybees have greater numbers and a more diverse set of tetracycline resistance genes than honeybees from the other countries.

" It is reasonable to expect to see widespread resistance among bees, considering the decades-long use of oxytetracycline in honeybee hives. 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.

The researcher noted that beekeepers have long used oxytetracycline to control the bacterium that causes foulbrood, but the pathogen eventually acquired resistance to tetracycline itself. 

"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," added Moran.

Countries like Switzerland, the Czech Republic and New Zealand do not allow beekeepers to use oxytetracycline in hives. As a result of which honeybees and wild bumblebees from these countries harbored only two or three different resistance genes and in very low copy numbers indicating that the bacteria did not require the genes very frequently.

The research highlights that by encouraging resistance and altering the bacteria that live in honeybee guts, decades of antibiotic applications may have actually been harmful to honeybee wellbeing.

The study shows, the bacterial residents of the honeybee gut play beneficial roles in neutralizing toxins in the bees' diet, nutrition  and in defending the bee against pathogens.  

Disrupting the honeybee microbiota and reducing its diversity, long-term antibiotic use could weaken honeybee resistance to other diseases. Hence, the treatment that was meant to prevent disease and strengthen the hive may actually weaken its ability to fight off other pathogens.

"These gut bacteria", said 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."

The study appears on October 30 in mBio, the online open-access journal of the American Society for Microbiology.--