Streptococcus lactis subsp. diacetylactis is well-known for its ability to inhibit pathogenic and milk spoilage microorganisms. In this study, an attempt was made to standardize the method for estimation of antimicrobial activity of the organism. Fourteen strains of S. lactis subsp. diacetylactis were examined for production of antimicrobial substances and all strains were found to produce antimicrobial substances. Of the strains, strain DRC1 produced maximum amounts of antimicrobial substances followed by strains DRC2 and S1. Mutants of S1 (S1-67/C and S1-195) produced higher amounts of antimicrobial substances than all other strains tested. The antimicrobial properties of strains S1-67/C were assessed against 28 bacterial and mold cultures. Cell-free filtrates of S1-67/C strain were more inhibitory to gram-negative than gram-positive bacteria. This organism also inhibited the growth of Geotrichum candidum but failed to inhibit other molds tested in this study.
1Present address: Department of Animal Products Technology, Faculty of Agriculture, Okayama University, Okayama-Shi-700, Japan.