Nova Scotian bees as sources of antimicrobial compounds against American foulbrood disease

Abstract

Honey bees, Apis mellifera, face many parasites and pathogens such as Paenibacillus larvae, the causal agent of American Foulbrood disease (AFB), a highly contagious disease. Honey bees rely on a diverse set of individual and group-level defenses to prevent disease. One route by which honey bees might combat disease is through the protective effects of their microbial symbionts. This study focuses on microbial interactions in bees that help in fighting AFB through the inhibition of P. larvae. Honey bees and wild bees in Nova Scotia were sampled for microbial isolation and screened against P. larvae using pairwise antimicrobial assay. Isolates showing good inhibition were chosen for extraction of metabolites with ethyl acetate and 1:1 chloromethane-methanol to obtain antimicrobial compounds that inhibit P. larvae. The extracts were analysed using LC/DAD and UHPLC/MS. Novel microbial species such as Pseudomonas chloroaphis, Debaromyces prosopidis and Paenibacillus lactis along with previously reported B. cereus and B. subitilis, were isolated from beehive swabs and showed strong inhibition against P. larvae. Chloroform: Methanol extracts of E8 that is a mixture of at least 6 microbial strains and of A12 showed strong inhibition while ethyl acetate extracts showed moderate inhibition against P. larvae. Our findings show great potential for discovery of novel antagonistic compounds against AFB.