Abstract:
Honeybee colonies offer an excellent environment for microbial pathogen
development. The highest virulent, colony killing, bacterial agents are Paenibacillus
larvae causing American foulbrood (AFB), and European foulbrood (EFB)
associated bacteria. Besides the innate immune defense, honeybees evolved
behavioral defenses to combat infections. Foraging of antimicrobial plant compounds
plays a key role for this “social immunity” behavior. Secondary plant
metabolites in floral nectar are known for their antimicrobial effects. Yet, these
compounds are highly plant specific, and the effects on bee health will depend
on the floral origin of the honey produced. As worker bees not only feed themselves,
but also the larvae and other colony members, honey is a prime candidate
acting as self-medication agent in honeybee colonies to prevent or decrease
infections. Here, we test eight AFB and EFB bacterial strains and the growth
inhibitory activity of three honey types. Using a high-throughput cell growth
assay, we show that all honeys have high growth inhibitory activity and the two
monofloral honeys appeared to be strain specific. The specificity of the monofloral
honeys and the strong antimicrobial potential of the polyfloral honey suggest
that the diversity of honeys in the honey stores of a colony may be highly
adaptive for its “social immunity” against the highly diverse suite of pathogens
encountered in nature. This ecological diversity may therefore operate similar
to the well-known effects of host genetic variance in the arms race between host
and parasite.
