Antimicrobial activity of allicin against honey bee pathogens
K A Aronstein and G W Hayes
Allicin is the chief antimicrobial compound produced in garlic. It has been studied for activities against human and food-born pathogens. In this study the antimicrobial activity of allicin (Allisure liquid) was tested against a number of bacterial and fungal pathogens (Paenibacillus larvae larvae, P. l. pulvifaciens, Ascosphaera apis and Ascosphaera aggregate) associated with social (Apis mellifera) and solitary bees. The minimum inhibitory concentrations (MIC) of allicin were determined using a broth microdilution method in the range of 1000 ppm to 0.25 ppm. Allicin liquid showed activity against gram positive bacterial isolates (MIC 350 ppm) and fungal isolates (MIC 250 ppm). The antimicrobial activity of allicin was also tested in an agar diffusion test using 250 µg of allicin per disk. Bacterial isolates (P. l. pulvifaciens and P. l. larvae) were associated with zones of inhibition in the range of 24-26 mm and 45-50 mm, respectively. The fungal isolates were associated with zones of inhibition in the range of 31-35 mm (A. apis) and 35-37 mm (A. aggregata). The macrolide class antibiotic tylosin (Tylan 50, Elanco Inc., IN) was used as a control in both the MIC assay and in the agar diffusion test. The data from this study point to the potential of allicin to inhibit growth of bee pathogens and reduce occurrence of at least two major bee diseases.