After Decades of Antibiotic Treatment of Honeybee Colonies, Tetracycline-resistant Bacteria Often Found in US Bees

After years of preventive treatment with antibiotics, the guts of domesticated honeybees in the United States harbor numerous genetic variants that confer resistance to the antibiotic tetracycline, a recent study found. Image: Agricultural Research Service/Jack Dykinga

First it was pigs and chickens that were found to harbor antibiotic-resistant bacteria as a consequence of widespread use of antibiotics in the animals for preventive purposes. Now researchers have discovered that honeybees similarly exposed to antibiotics for decades carry bacteria in their guts that are resistant to tetracycline, according to a study published online today in the journal mBio.

The finding of antibiotic-resistant bacteria in honeybees doesn’t pose a direct threat to human health because these bacteria are not found in the honey produced by the bees. But the study provides insights into the consequences that widespread antibiotic use can have on gut flora and health in another species.

For more than 50 years, US beekeepers have applied oxytetracycline to honeybee colonies to prevent a bacterial disease called foulbrood. To assess the effect of this use on the gut bacteria of bees, a team of researchers used genetic sequencing and other techniques to compare bacteria in the gut of US domesticated bees, wild bees (which presumably wouldn’t be exposed to the antibiotic), and domesticated bees from parts of Europe and New Zealand where use of antibiotics on bees has been forbidden. The researchers found that gut bacteria in US bees carry 8 genetic variants that confer resistance to tetracycline, compared with 1 or 2 such resistance-conferring variants in wild bees or in those from countries that don’t use antibiotics on bees.

Honeybees throughout the United States carry the resistant bacteria, said senior author Nancy Moran, PhD, of Yale University, in a statement. “There’s a pattern here, where the US has these genes and the others don’t.”

Of particular concern was the finding that 1 resistance-conferring gene variant found in bee gut bacteria is also found in the foulbrood bacteria, which are now also tetracycline resistant. Moran said it is possible this variant was transferred from the gut bacteria to the pathogen or vice versa.

Moran and her colleagues noted that bees, which have a small and well-characterized number of gut bacteria, provide a good model for understanding the long-term effect of antibiotic use on gut bacteria.

“Prolonged exposure to a single broad-spectrum antibiotic imposes strong selective pressure on a microbial community that is expected to result in loss of strain diversity….” the authors conclude. “These shifts could affect host health: in the case of the distinctive gut bacteria of honeybees and bumblebees, metagenomic and experimental studies suggest beneficial roles [of the gut bacteria] in neutralization of dietary toxins, nutrition, and in defense against pathogens.”

Categories: Adverse Effects, Occupational and Environmental Medicine

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