Anti-fungal activity of lactic acid bacterial isolates against aflatoxigenic fungi inoculated on peanut kernels

Aflatoxigenic fungi infect various agricultural commodities and produce a class I carcinogen aflatoxin B1 (AFB1). Sixteen bacterial isolates were screened from idli batter and other fermented foods, for antagonistic effect against Aspergillus spp. Based on the preliminary observation, three bacterial isolates from idli batter namely, IB1, IB4, IB7, and one from mango wine namely, MW2 were selected and further characterized. IB1 was found to be closely related to Lactobacillus plantarum argentoratensis while IB4, IB7, and MW2 were closely related to Enterococcus faecium according to their 16sRNA sequencing. Invitro and invivo antifungal tests in peanut revealed that cell free supernatant (CFS) obtained from these isolates inhibited fungal growth and significantly suppressed AFB1 production, and expression of aflD, aflP, OrdB and aflR genes. Further, microscopic examination showed that all isolates could reduce the conidial development and inhibits spore formation. The highest antifungal activity was observed in CFS of L. plantarum MN880325 and E. faecium MN880376, with an inhibition zone of >= 28 mm in PDA and >= 97% reduction in aflatoxin production on peanut kernels. ESI-MS and NMR spectroscopy revealed the active compounds from L. plantarum MN880325 and E. faecium MN880376 to be 3-phenyllactic acid and 4-hydroxyphenyllactic acid respectively.