Bacteriocin Produced by Streptococcus thermophilus against Bifidobacterium Species

Abstract

This study was carried out to evaluate the antagonistic relationship between yogurt and probiotic bacteria and the nature of the inhibitory compound produced by the organisms. Eight strains each of Streptococcus thermophilus, Lactobacillus delbrueckii subsp. bulgaricus, Lactobacillus acidophilus and bifidobacteria were isolated from eight commercial AB (L. acidophilus and Bifidobacterium spp.) products containing these four groups of bacteria. The isolates were screened for the production of bacteriocins against each of the 8 isolates of L. acidophilus and Bifidobacterium spp. Twelve strains showed inhibitory activity against all the 8 strains of Bifidobacterium spp. and 5 L. acidophilus isolates with the 'spot on lawn' assay. Of these, only one yogurt bacterium, S. thermophilus was identified to be a bacteriocinproducing organism. The S. thermophilus strain was found to specifically target 2 strains of bifidobacteria. The crude antimicrobial compound was found to be heat stable, resistant over a wide range of pH, and sensitive to proteolytic enzymes, but it retained activity after treatment with lipase. The compound was purified using ultrafiltration, precipitation with ammonium sulfate and dialysis. The bacteriocin-fractionate was also subjected to SDS-PAGE analysis and the molecular weight of the bacteriocin was estimated to be approximately 80 kDa.