This study was performed to determine the antibacterial activity of methanol extracts of 23 bryophyte species against Paenibacillus larvae isolates that cause American foulbrood diseases in honeybee larvae. The honey and larva samples were collected from nine different locations of Rize in Turkey. A total of 22 gram-positive spore-forming bacteria were isolated from the larva and honey samples. According to the results of morphological, biochemical, and molecular (16S rRNA gene sequencing) tests, 10 isolates of the 22 gram-positive spore-forming bacteria were identified as P. larvae. A total of 10 bryophyte species (Polytrichum formasum, Polytrichum commune, Calliergonella cuspitada, Calliergonella lindbergi, Metzgeria conjugata, Isothecium alopecuroides, Syntrichia calcicola, Syntrichia intermedia, Tortella densa, and Grimmia alpestris) among 23 bryophytes showed good antimicrobial activity against P. larvae isolates according the results of agar-well diffusion method and minimal inhibition concentration experiments.

Bee disease caused by spore-forming Paenibacillus larvae and Paenibacillus alvei is a serious problem for honey production. Thus, there is an ongoing effort to find an effective agent that shows broad biocidal activity with minimal environmental hazard. In this study, the biocidal effect of maltose reduced silver nanoparticles (AgNPs) is evaluated against American foulbrood and European foulbrood pathogens. The results demonstrate that the maltose reduced AgNPs are excellent short and long-term biocides against P. larvae isolates. The long-term effect suggests that the Ag ions are released from the AgNPs with increasing time in a controlled manner.

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