Purpose: This study is to explore the potential of using vegetable-associated Bacillus subtilis strains as bio-agents to prevent the internalization of Salmonella spp. in growing mung bean sprouts.
Methods: With the deferred agar spot method, Bacillus subtilis strains isolated from lettuce and mung bean seeds were screened for antimicrobial activities against common foodborne pathogens, including strains of Salmonella spp., Shiga toxin-producing Escherichia coli, and Listeria monocytogenes.
To evaluate the efficacy of the B. subtilis isolate LCA 1 for inhibiting the internalization of Salmonella spp. in growing mung bean sprouts, mung bean seeds were incubated with the LCA 1 culture suspension and then inoculated with cells of S. enterica ser. Typhimurium ATCC14028 before sprouting. The spouts were withdrawn at predefined intervals to enumerate the Salmonella Typhimurium by plating sprout homogenates on selective agar plates after surface sanitization.
Results: The B. subtilis isolate LCA1 showed broad inhibition spectrum against Salmonella spp., E. coli, and L. monocytogenes with the radii of the inhibition zones ranging from 2 to 13 mm on the agar plates. The B. subtilis isolate LCA1 significantly reduced the internalized Salmonella load in the growing spouts. The maximal reduction occurred at day 2 of sprouting, where the LCA1-treatment group appeared to have 60 times fewer internalized Salmonella load, compared with the control group.
Significance: The results suggest that the vegetable-associated Bacillus subtilis LCA 1 may be used as a bio-agent to control internalization of foodborne pathogens in growing mung bean sprouts.