Antimicrobial activity of Bacillus amyloliquefaciens EMD17 isolated from Cheonggukjang and potential use as a starter for fermented soy foods.

A Bacillus strain with antimicrobial activity was isolated from Cheonggukjang and identified as Bacillus amyloliquefaciens. Filtered culture supernatants of B. amyloliquefaciens EMD17 strongly inhibited growth of Bacillus cereus ATCC14579, Listeria monocytogenes ATCC19111, and an ochratoxin (OTA) producing Penicillium spp. The antimicrobial activity was not decreased by heat, pH, and proteases treatment, indicating a non-proteinous nature of the antimicrobial substance. A B. amyloliquefaciens EMD17 culture added to a B. cereus ATCC14579 culture killed B. cereus cells completely in 6 h, showing the bacteriocidal effect. The srfAA gene encoding surfactin synthetase A was detected using PCR, indicating that surfactin might be the responsible agent. Genes encoding fengycin and iturin were also detected. MS indicated production of lipopeptides, including surfactin. Cheonggukjang and Doenjang were prepared using B. amyloliquefaciens EMD17 as a starter and growth of spiked B. cereus cells was completely inhibited.