Antimicrobial activity of lactobacilli and streptococci

Of nine strains of lactic acid bacteria commonly used as starter cultures for the dalry industry and ensiling, six (Lactobacillus bulgaricus, L. casei, L. acidophilus CH=5, L. plantarum, Streptococcus latis and Strep. taecium) had antibiotic activity. Gram-positive bacteria were more sensitive than Gram-negative bacteria to the antibiotics. The most sensitive strain of Staphylococcus aureus was used as a target micro-organism for the characterization of the antimicrobial substance. The cultures of Streptococcus faecium and L. plantarum gave the most intense antimicrobial activity. Adding CaCO3 to the medium (to bind accumulated lactic acid) increased the antibiotic activity of the lactic acid bacteria.