Production of growth-inhibiting factors by Lactobacillus delbrueckii

Aims: The detection of growth-inhibiting. factors produced by Lactobacillus delbrueckii. Methods and Results: A bioscreen assay was developed to study the effect of Lact. delbrueckii culture supernatant fluids on the growth of phylogenical ly or functionally related bacteria in broth cultures. Several growth-inhib iting factors could be distinguished based on differential effects on diffe rent test strains, separation by ultrafiltration and sensitivity to heat, p roteinase treatment or catalase addition. Conclusions: Lactobacillus delbrueckii strain VI1007 was found to produce a t least three growth-inhibiting factors, other than lactic acid, when grown under microaerobic conditions in MRS broth. These included H2O2 and a bact eriocin-like, heat- and proteinase-sensitive bactericidal molecule or compl ex with a molecular weight greater than 50 kDa. A third factor inhibited th e growth of Streptococcus thermophilus. Significance and Impact of the Study: The assay system used allows the dete ction of subtle interactions between strains, that are likely to be of ecol ogical importance in mixed cultures but would go unnoticed in classical aga r diffusion tests.