Antibiotics May Cause Bees More Harm Than Good

Honeybees treated with a common antibiotic (with pink dots) were half as likely to survive the week after treatment compared with a group of untreated bees (green dots). Credit: Vivian Abagiu/University of Texas at Austin

(CN) – Honeybees treated with a common antibiotic were half as likely to survive the week after treatment as a group of untreated bees – a concerning trend that may affect humans as well.

Scientists from the University of Texas at Austin found that the antibiotics removed beneficial gut bacteria in the bees, which allowed a harmful pathogen to take root. The team published their findings Tuesday in the journal PLOS Biology.

The overuse of antibiotics is a major dilemma within modern medicine – successfully treating a variety of health conditions often requires them, but repeatedly prescribing them gradually reduces their effectiveness and leaves the general population at risk of developing more severe, and potentially untreatable, illnesses.

The team treated the bees with the common antibiotic tetracycline, which dramatically reduced naturally occurring gut microbes – healthy gut bacteria that can help block pathogens, promote absorption of nutrients from food and more. The researchers also found elevated levels of Serratia, a pathogenic bacterium that can affect humans and other animals, in the bees treated with the antibiotic.

The findings are important for the agriculture industry and beekeepers in the aftermath of finding their hives destroyed by what officials termed “colony collapse disorder.” This phenomenon led to millions of bees mysteriously disappearing, leaving farms with fewer pollinators for crops.

A handful of explanations for colony collapse disorder were presented at the time. However, scientists now believe antibiotics given to bees could also have played a role.

“Our study suggests that perturbing the gut microbiome of honeybees is a factor, perhaps one of many, that could make them more susceptible to declining and to the colony collapsing,” co-lead author and UT Austin professor Nancy Moran said. “Antibiotics may have been an underappreciated factor in colony collapse.”

Bees are a helpful model for the human gut as they share a natural community of microbes in their guts called a microbiome, which aids a number of functions including development and immunity. Both also have specialized gut bacteria, which live only in the host gut. These gut bacteria are passed from individual to individual during social interactions.

The team’s findings suggest the overuse of antibiotics may increase the likelihood of infections from pathogens.

“We aren’t suggesting people stop using antibiotics. Antibiotics save lives. We definitely need them,” Moran said. “We just need to be careful how we use them.”

In large-scale agriculture, beekeepers generally apply antibiotics to their hives several times a year in order to prevent bacterial infections that can lead to a disease breakout that harms bee larvae.

“It’s useful for beekeepers to use antibiotics to protect their hives from foulbrood,” said Kasie Raymann, co-lead author and postdoctoral researcher at UT Austin. “But this work suggests that they should also consider how much and how often they’re treating hives.”

The team removed hundreds of bees from long-established hives on the rooftop of a university building and brought them to a lab, where some were fed a sweet syrup with antibiotics while others were fed syrup only. The researchers painted small colored dots on the bees’ backs to identify which subjects had received antibiotics and which had not.

After five days of daily treatment, the bees were returned to their hives. Over the next few days, the team then collected the treated and untreated bees to sample their gut microbes and determine how many were still living.

Roughly two-thirds of the untreated bees were still present, while only about one-third of the bees treated with antibiotics were still present.

“This was just in bees, but possibly it’s doing the same thing to you when you take antibiotics,” Raymann said. “I think we need to be more careful about how we use antibiotics.”