Antibacterial activity of sourdough lactic acid bacteria: Isolation of a bacterioincin-like inhibitory substance from Lactobacillus sanfrancisco C57

A total of 232 strains from nine species of Lactobacillus isolated from sourdoughs were screened for antagonistic activity against sourdough-related micro-organisms. Seventy-seven strains on agar medium and 52 in culture supernatants, re-adjusted to pH 6.5 and catalase-treated, showed antagonistic activity. The activities were species and strain specific showing different spectra of inhibition against sourdough lactobacilli. All the strains were inhibitory to Bacillus subtilis but not against sourdough yeasts and moulds. Lactobacillus sanfrancisco and Lactobacillus plantarum strains had the largest inhibitory spectrum. All the antimicrobial compounds produced from strains of different species contained a protein moiety and were differently sensitive to different proteinases. A bacteriocin-like inhibitory substance, which was heat-stable (100 degrees C for 20 min), insensitive to lipase and alpha-amylase, of a protein nature, with an inhibitory spectrum centred about lactic acid bacteria and a bactericidal or bacteriolytic mode of action was isolated from Lb. sanfrancisco C57. The antimicrobial substance also inhibited Listeria monocytogenes, and was mainly produced in the stationary phase of growth and at pH 4.0-5.0. Lb. sanfrancisco C57 variants, which did not contain the native c. 17 kbp plasmid, maintained their antagonistic activity, therefore, the gene encoding for the bacteriocin-like inhibitory substance from Lb. sanfrancisco C57 is chromosomally located. (C) 1996 Academic Press Limited