AUTHOR=Gollop Rachel , Kroupitski Yulia , Matz Ilana , Chahar Madhvi , Shemesh Moshe , Sela Saldinger Shlomo 

TITLE=Bacillus strain BX77: a potential biocontrol agent for use against foodborne pathogens in alfalfa sprouts

JOURNAL=Frontiers in Plant Science

VOLUME=15

YEAR=2024

URL=https://www.frontiersin.org/journals/plant-science/articles/10.3389/fpls.2024.1287184

DOI=10.3389/fpls.2024.1287184

ISSN=1664-462X

ABSTRACT=<p>Despite regulatory and technological measures, edible sprouts are still often involved in foodborne illness and are considered a high-risk food. The present study explored the potential of spore-forming <italic>Bacillus</italic> isolates to mitigate <italic>Salmonella</italic> and <italic>Escherichia coli</italic> contamination of alfalfa sprouts. Food-derived <italic>Bacillus</italic> strains were screened for antagonistic activity against <italic>S. enterica</italic> serovar Typhimurium SL1344 (STm) and enteropathogenic <italic>E. coli</italic> O55:H7. Over 4 days of sprouting, levels of STm and <italic>E. coli</italic> on contaminated seeds increased from 2.0 log CFU/g to 8.0 and 3.9 log CFU/g, respectively. Treatment of the contaminated seeds with the most active <italic>Bacillus</italic> isolate, strain BX77, at 7 log CFU/g seeds resulted in substantial reductions in the levels of STm (5.8 CFU/g) and <italic>E. coli</italic> (3.9 log CFU/g) in the sprouted seeds, compared to the control. Similarly, co-culturing STm and BX77 in sterilized sprout extract at the same ratio resulted in growth inhibition and killed the <italic>Salmonella</italic>. Confocal-microscopy experiments using seeds supplemented with mCherry-tagged <italic>Salmonella</italic> revealed massive colonization of the seed coat and the root tip of 4-day-old sprouted seeds. In contrast, very few <italic>Salmonella</italic> cells were observed in sprouted seeds grown with BX77. Ca-hypochlorite disinfection of seeds contaminated with a relatively high concentration of <italic>Salmonella</italic> (5.0 log CFU/g) or treated with BX77 revealed a mild inhibitory effect. However, disinfection followed by the addition of BX77 had a synergistic effect, with a substantial reduction in <italic>Salmonella</italic> counts (7.8 log CFU/g) as compared to untreated seeds. These results suggest that a combination of chemical and biological treatments warrants further study, toward its potential application as a multi-hurdle strategy to mitigate <italic>Salmonella</italic> contamination of sprouted alfalfa seeds.</p>