Distinct anti-biofilm mechanisms of Bacillus amyloliquefaciens D747 against Salmonella enterica and Listeria monocytogenes

Bacillus amyloliquefaciens is a robust biocontrol agent widely utilized against fungi and other plant pathogens. This study evaluated the antagonistic potential of the EPA-registered strain B. amyloliquefaciens D747 (Ba D747) against Salmonella enterica and Listeria monocytogenes biofilms. Co-cultivation with Ba D747 significantly inhibited bacterial growth and reduced biofilm populations on glass and on stainless steel surfaces. Mechanistic assays revealed distinct, pathogen-specific dual-mode actions. Inhibition of L. monocytogenes was primarily driven by secreted metabolites, with Ba D747 cell-free supernatants exhibiting potent bactericidal activity. Conversely, Ba D747 cell-free supernatants had minimal impact on S. enterica growth, and the segregation of Ba D747 and Salmonella cells through a cell impermeable membrane strongly diminished Ba antagonistic activity, suggesting a contact-dependent antagonism as the critical driver for Salmonella suppression. These results demonstrate that Ba D747 utilizes a combination of secreted factors and physical dominance to outcompete resilient foodborne pathogens, offering a sustainable and safe biological intervention for food processing environments.