Nature of the antimicrobial activity of Lactobacillus casei, Bifidobacterium bifidum and Bifidobacterium animalis against foodborne pathogenic and spoilage microorganisms.

The antimicrobial activities as well as the nature of the inhibitory compounds obtained from Lactobacillus casei, Bifidobacterium bifidum and Bifidobacterium animalis strains were assayed on foodborne pathogenic - Staphyloccoccus aureus subsp. aureus (CCUG ATCC® 25926™) and Escherichia coli (ATCC® 25922™) - and spoilage microorganisms - Pseudomonas aeruginosa (ATCC® 27853™). Test producer strains showed inhibitory effect on all indicator microorganisms in diffusion of cell-free concentrated supernatant by agar in well methods (10.0-22.5 mm) in periods of 24, 48 and 72 h. Inhibitory compounds showed no sensitivity to the action of proteolytic enzyme trypsin and were completely inactivated by adjusting the pH of the cell-free 20 × concentrated supernatant to 7.0. The results demonstrated that antimicrobial substances do not have proteinaceous nature and are caused by the action of organic acids with decreasing medium pH.