Adding probiotics to honeybees' food helps make them more resistant to nosemosis, a fungal infection associated with colony collapse disorder (CCD) that has been observed in Europe and North America over the past 20 years, according to an announcement from Université Laval in Quebec City, Que.

Probiotics can decrease the mortality rate of this infection in bees by up to 40%, the researchers reported in the most recent edition of Frontiers in Ecology & Evolution.

Nosemosis, also called nosema disease, is caused by Nosema ceranae, a single-celled fungus of Asian origin that bees ingest with their food and that grows in the cells of their intestinal walls, the researchers said.

"Under normal conditions, this fungus does not cause any problems for bees," explained Nicolas Derome, professor with the Université Laval faculty of science and engineering and lead author in the study. "When bees are subjected to stress, the microorganism can evade their immune system, causing an infection that can impair their ability to forage, hinder larval care, disturb the bees' orientation and increase mortality."

Currently, nosemosis is treated with antibiotics, but their efficacy is declining as resistant strains of the fungus have emerged. "In addition, these products can kill beneficial bacteria in the intestinal microbiota of bees," Derome said. "We had to find other solutions to combat this disease, and that's what gave us the idea to test probiotics."

The researchers measured the effectiveness of four probiotics on the prevention and treatment of nosemosis in bees placed in laboratory cages. Two of these probiotics were commercial products used on pork, chicken, shrimp and salmonid farms. The other two probiotics were bacteria that researchers have isolated from the intestinal microbiota of healthy bees. The four probiotics were mixed with sugar syrups and administered to the bees.

After two weeks of testing, the researchers found that the mortality rate of infected bees was 20-40% lower in those receiving probiotics than in the control group, the researchers said, noting that the four probiotics tested showed similar efficacy.

"Our results suggest that bacteria in the microbiota of bees can be as effective as commercial probiotics in treating nosemosis," Derome said. "It's important to note that given a very high infection rate, the probiotics tested did not reduce the number of fungi present in bees, but they allowed the bees to better tolerate them."

Derome and his team said they intend to take advantage of the protective properties of the probiotics present in bees' microbiota to develop new ways of combating nosemosis.

"The tests we've conducted in bee colonies suggest that a particular probiotic, called Parasaccharibacter apium, is our best candidate. We have also identified other promising microbial strains and now hope to develop a combination of probiotics to combat nosemosis in bees. However, the real solution to this disease is to identify and correct the sources of stress disrupting the bees," Derome concluded.