Antibiotics play a critical role in managing bacterial and parasitic infections that may threaten colony health. They are an important tool that beekeepers use to manage disease, but their effects can extend beyond harming pathogens. These treatments may also disrupt the beneficial microbes that bees rely on for digestion, immunity and survival.
Bee-ware: Antibiotics and Gut Health
To treat Nosema disease in honey bees, the only approved antimicrobial in North America is Fumagillin-B ®. This compound, derived from the fungus Aspergillus fumigatus, has been shown to reduce the prevalence and intensity of Nosema spp. infections 1. Fumagillin is typically administered in the fall or spring, depending on colony needs and label recommendation 1. Fumagillin-B works by targeting a protein in the parasite called methionine aminopeptidase type 2 (MetAp-2) 2 . This protein is essential for Nosema spp. spore development, and by inhibiting it, Fumagillin disrupts the parasite’s life cycle 2.
Figure 1: Picture of Nosema spp. spores viewed under a microscope (400x). As an example, the arrow indicates a single spore (ATTTA©, 2025)
Another antibiotic that is used in beekeeping is oxytetracycline hydrochloride (OTC). It has been used to manage European Foulbrood (EFB) and American Foulbrood (AFB) 3. Oxytetracycline works as a bacteriostatic antibiotic, meaning it restricts the bacteria from growing and interferes with protein synthesis 3. However, it has also been found to reduce core gut bacteria like Bifidobacteria , which supports digestion and immune signaling 4. Bifidobacteria is an important bacterium that plays a role in the digestion and metabolism of a variety of plant-produced carbohydrates 8.
This disruption of the gut microbiome, known as dysbiosis, can have serious consequences. For example, a study showed that honey bees treated with an antibiotics, penicillin-streptomycin, showed reduced expression of genes responsible for producing antimicrobial peptides (AMPs), compared to bees who were infected with Nosema ceranae 5. This can lead to a weakened immune system, as AMPs play a critical role in immune defense 5. Another study found that bees infected with Nosema spp. and treated with antibiotics had higher spore loads and more severely disrupted gut bacteria 6. Long-term use of antibiotics like oxytetracycline has also been linked to a reduction in genetic diversity among core bacteria, such as Gilliamella 7. This bacterium is important for producing pyruvate, which is essential for the break down of glucose 11.
The effects of dysbiosis go beyond just gut health. A disrupted microbiome, whether caused by disease or antibiotics, may lead to greater susceptibility to pathogens, disrupted expression of developmental genes, and compromised immune function 8. Disruption of the gut microbiome has also been associated with increased loads of other parasites, such as Lotmaria passim, in adult honey bees 9. These effects can weaken the entire colony, especially if antibiotics are used without a plan.
Another concern with frequent antibiotic use is the development of antibiotic resistance. In both North America and Argentina, where oxytetracycline is commonly used, resistance has been reported in Paenibacillus larvae, the bacteria which causes American Foulbrood 9. Following antibiotic use, resistance genes in the gut microbiome have been shown to increase 10. These genes may spread between colonies through cross-contamination, and residues of antibiotics have been detected in the environment 9. When antibiotics are overused, pathogens can evolve resistance, making it significantly more difficult to treat infections effectively.
That is why it is so important to only treat when necessary and to support bees afterwards. A healthy gut microbiome is one of the best defenses bees have against diseases. Unnecessary antibiotic use can compromise colony health by disrupting the balance in the bee’s gut microbiome. Maintaining a healthy gut year-round helps reduce the pressure of pathogens and the need for antibiotics. There are other ways to ensure gut health is being supported in bees, which will be discussed in a future blog.
Written by Kaitlyn Newton, ATTTA Seasonal Apiculturist
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References:
1.
Prouty, C., Jack, C., Sagili, R. and
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11. Kešnerová, L., Mars, R.A., Ellegaard, K.M., Troilo, M., Sauer, U. and Engel, P., 2017. Disentangling metabolic functions of bacteria in the honey bee gut. PLoS biology, 15(12), p.e2003467.
