Inhibition of the American foulbrood bacterium, Paenibacillus larvae larvae, by bacteria isolated from honey bees

While honey bees (Apis mellifera) support a diverse microbial community, the impacts of most of their associated microbes on honey bee health remain unresolved. Here, pairwise inhibition assays were used to identify honey bee bacterial symbionts that inhibit a primary pathogen, the Gram-positive bacterium Paenibacillus larvae larvae. Four bacterial taxa isolated from bee larvae appeared especially promising with respect to inhibition of P.I. larvae and, in fact, completely inhibited P L larvae growth in pairwise plate assays. These isolates were identified by 16S ribosomal RNA sequencing as Stenotrophomonas maltophilia, Acinetobacter sp., Brevibacillus formosus and Bacillus fusiformis. A PCR-based survey confirmed that these bacterial isolates are present in bee larvae, at frequencies ranging from 2% (1/48) for B. formosus to 79% (39/48) for Acinetobacter sp. An understanding of the distributions of these co-occurring bacteria could elucidate variation across colonies in susceptibility to American foulbrood disease. In addition, supplementation of colonies with these naturally occurring bacteria or their antagonistic products can provide a novel way of controlling foulbrood disease.