Efficiency of bacteria strain Streptococcus thermophilus for producing bacteriocin-like substance to inhibit the pathogenic bacteria growth

Abstract

Bacteriocin is synthesized from microorganisms, especially lactic acid bacteria. This substance can inhibit some foodbone pathogenic bacteria in human such as Salmonella typhimurium and Staphylococcus aureus. Thus, this research was aims to estimate the ability of lactic acid bacteria strain S. thermophilus found in commercial fermented milk product to construct bacteriocin-like substance for inhibiting pathogenic bacteria growth. Fermented milk produced with S. thermophilus was cultured the bacteria with deMan Rogosa Sharp (MRS) medium. Pure culture was established its growth and bacteriocin-like substance using MRS broth and UHT milk. The activity of this substance to inhibit pathogenic bacteria S. typhimurium and S. aureus was measured by agar well diffusion method. The results stated that S. thermophilus cultured with MRS broth higher grew (log 10.0 cfu/ml) than UHT milk (log 9.0 cfu/ml) at 24 hours after incubation. On the other hand, pH value was rapidly decreased as high acid pH 4.0 when S. thermophilus was cultured with UHT milk for 24 hours after incubation. Bacteriocin-like substance produced by S. thermophilus in UHT milk (2 hours) was rapidly detected more than MRS broth (10 hours). Average activity of this substance to inhibit S. aureus was higher than S. typhimurium by showing the highest activity as 200 AU/ml.