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.