Inhibition of Paenibacillus larvae by lactic acid bacteria isolated from fermented materials.

We evaluated the potential application of lactic acid bacteria (LAB) isolated from fermented feeds and foods for use as probiotics against Paenibacillus larvae, the causal agent of American foulbrood (AFB) in vitro. We also assessed the ability of LAB to induce the expression of antimicrobial peptide genes in vivo. Screening of the 208 LAB isolated from fermented feeds and foods revealed that nine strains inhibited the in vitro growth of P. larvae. The LAB strains were identified by 16S rRNA gene sequencing as Enterococcus sp., Weissella sp. and Lactobacillus sp. These strains were screened for their abilities of immune activation in honeybees by real-time RT-PCR using antimicrobial peptide genes as markers. After oral administration of several of the screened LAB to larvae and adults, the transcription levels of antimicrobial peptide genes, such as abaecin, defensin and hymenoptaecin, were found to increase significantly. These findings suggested that selected LAB stimulate the innate immune response in honeybees, which may be useful for preventing bacterial diseases in honeybees. This is the first report to characterize the probiotic effects of LAB isolated from fermented feeds and foods in honeybees.