Antibacterial potential of lactobacilli isolated from a lamb

The antimicrobial properties of three potential probiotic strains of lactobacilli isolated from a lamb (Lactobacillus murinus C, Lactobacillus mucosae D and Lactobacillus reuteri E) were studied using the streak line method and the agar well diffusion assay. The probiotic lactobacilli strains Lactobacillus rhamnosus ATCC 53103, Lactobacillus reuteri ATCC 55730, Lactobacillus reuteri ATCC 55845 and Lactobacillus plantarum DSM 9843 were used for comparison. Using the streak line method the inhibitory activity of lactobacilli products towards ten Gram-positive and Gram-negative potential pathogenic bacteria under different cultivation conditions (anaeorobic or microaerobic preincubation of lactobacilli for 24 h or 48 h) was tested. The strongest inhibitory activity was demonstrated by the Lactobacillus reuteri E strain. The most sensitive strains to the antimicrobial activity of lactobacilli were Yersinia enterocolitica clinical isolate (19.9 ± 6.8 mm) and Listeria monocytogenes ATCC 51774 (17.7 ± 6.0 mm) after microaerobic and anaerobic preincubation, respectively. Generally, microaerobic conditions and longer preincubation of lactobacilli resulted in stronger inhibition of target bacteria. The inhibitory activity of lactobacilli towards selected lactobacilli strains was also tested. Only low inhibition of growth was observed. In the agar well diffusion assay the inhibitory effect of natural and modified lactobacilli culture cell-free supernatants, obtained from MRS broth cultures, on Staphylococcus aureus ATCC 6538 growth was determined. Supernatants were modified by heat (10 min/60 °C; 60 min/100 °C) and protease treatment and neutralization of pH. Neutralization elicited the most significant impact on the activity of supernatants and resulted in total loss of activity. After all other modifications supernatants retained some residual activity. The highest inhibitory activity was observed for the cell-free supernatant produced by Lactobacillus mucosae D.