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US honeybees becoming antibiotic resistant

05 Feb, 2013

Recent research by scientists from the Department of Ecology and Evolutionary Biology at Yale University has shown that bacteria in the guts of honeybees are highly resistant to the antibiotic tetracycline.

The scientists have identified eight different tetracycline-resistance genes among US honeybees that were exposed to the antibiotic. They noted that these genes were largely absent in bees from countries where such antibiotic use is banned, including New Zealand, Switzerland and the Czech Republic.

Use of antibiotics in US hives

In a press release from the American Society for Microbiology, one of the senior researchers, Professor Nancy Moran said, “It [resistance] seems to be everywhere in the US. There’s a pattern here, where the US has these genes and the others don’t.”

The antibiotic used in US hives since the 1950s is oxytetracycline, but genes that confer resistance to oxytetracycline also confer resistance to tetracycline. Tetracycline is commonly prescribed to humans.

Oxytetracycline is routinely used as a preventative in US hives to combat a larval disease called ‘foulbrood’, caused by the bacteria Melissococcus pluton and Paenibacillus larvae, which can wipe out a whole hive if infected.

Bees’ gut bacteria acquire antibiotic resistance

Professor Moran notes that the pathogens that cause foulbrood have now also acquired resistance to tetracycline. Of the foulbrood pathogens, Melissococcus pluton and Paenibacillus larvae both now carry tetL, “one of the eight resistance genes we found. It’s possible that the gene was transferred either from the [bee’s] gut bacteria to the pathogen or from the pathogen to the gut bacteria.”

In their published paper, the researchers write that, following the “emergence of resistance to oxytetracycline in P. larvae in 1996, alternative antibiotics were tested for its control. In October 2005, Tylosin was approved by the US Food and Drug Administration for use in beekeeping and was marketed to beekeepers. In 2007, accelerated losses of colonies occurred throughout the United States – the causes of these losses are not clear but appear not to be attributable to spread of a particular pathogen. Speculatively, disruption of the gut microbiota by a novel antibiotic might contribute to the decline of colonies of bees, with such effects potentially becoming less pronounced as members of the microbiota acquire resistance capabilities.”

Professor Moran says the results are not terribly surprising. “It parallels findings in other domestic animals, like chickens and pigs,” she says.

Long-term antibiotic use weakens bees’ resistance to diseases

The researchers point out that, by inadvertently promoting antibiotic resistance and altering the bacteria that live in honeybee guts, decades of antibiotic applications may have actually been detrimental to honeybee wellbeing. Studies have suggested that the bacterial residents of the honeybee gut play beneficial roles in neutralising toxins in bees’ diet, nutrition and in defending the bee against pathogens. By disrupting the honeybee microbiota and reducing its diversity, long-term antibiotic use could weaken honeybee resistance to other diseases.

No risk to honey-eating humans

Professor Moran says that, while the study is interesting from the perspective of honeybee health and has implications for how honeybee diseases are managed, the presence of resistant genes in the honeybee gut doesn’t pose a direct risk to humans. “These gut bacteria 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 research was published in the November/December 2012 issue of mBio, an open-access journal published by the American Society for Microbiology.

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