ANTIMICROBIAL ACTIVITY OF LACTIC CULTURES: PARTIAL PURIFICATION AND CHARACTERIZATION OF ANTIMICROBIAL COMPOUND(S) PRODUCED BY Streptococcus thermophilus

Abstract

Skim milk fermented by various lactic cultures was tested for antimicrobial activity by agar diffusion technique, using Pseudomonas jluorescens, P. aeruginosa and Bacillus subtilis as test organisms. Lactobacillus bulgaricus, L. acidophilus and Streptococcus thermophilus strongly inhibited the growth of the test organisms. Other lactic cultures, singly or in combination, showed varying degrees of antimicrobial activity. A methanoi-acetone (M-A) extract was prepared by lyophilizing fermented milk and extracting the powder sequentially with cold methanol and acetone. The methanol-acetone (M-A) extract strongly inhibited the growth of B. subtilis, B. pumulis, P. aeruginosa, P. jluorescens, Flavobacterium capsulatum, Satmonella typhimurium, Escherichia coli, Shigella sp. and Streptococcus lactis. The antimicrobial activity of S. thermophilus was not reported in the literature previously. The M-A extract contained ninhydrin-positive materials and did not lose antimicrobial activity even when it was exposed to a temperature of 100°C for 10 min. Five milliliters of M-A extract were applied to 20 x 2.2 cm Sephadex G-10 column equilibrated with 0.05N HCl which later served as the eluant. Fractions of 15 ml were collected at a flow rate of 2.5 ml/mm Sephadex fractionation of M-A extract showed that there were at least three active fractions. One of the fractions appeared in the void volume followed closely by the other fractions indicating that the latter two fractions have compounds of molecular weight less than 700 daltons. The purification achieved was about 400-fold. The activity (recovery) of the compound(s) increased upon fractionation on Sephadex indicating the possible presence of inhibitor(s).

Inhibiting factors produced by lactic acid bacteria. 2. Bacteriocins and other antibacterial substances

“…8ikes and Hilton (1987) extended the study of this spectrum and showed that the M-A extract was also active against Clostridium perfringens, Staphylococcus aureus and Salmonella enteritidis. The partial purification of inhibitory substances by gel filtration led to elution of a 700-Da molecular weight substance with antibacterial activity (Pulusani et al, 1979). The results, however, did not enable the authors to determine whether 1 or 2 compounds were involved in the inhibitory activity.…”

Purification and characterization of thermophilin ST-1, a novel bacteriocin produced by Streptococcus thermophilus ACA-DC 0001

“…The ability of various S. thermophilus strains to produce several antibacterial agents has been studied in the past [1,5,18,24,36,38]. The aim of this study was to purify and characterize a new bacteriocin produced by the "wild" strain S. thermophilus ACA-DC 0001, isolated from traditional Greek yogurt.…”

Modeling the kinetics of survival of Staphylococcus aureus in regional yogurt from goat's milk

“…Pazakova (1997) showed that the reduction of the number of staphylococci in the yogurt may be associated with low pH of the product. The authors describe the effect of metabolites produced by the fermentation cultures as a major factor inhibiting pathogenic microbes (Dahiya and Speck 1968, Pulusani et al 1979, Pazakova et al 1997. Therefore, it can be assumed that the substances produced by the strains used for the production of yogurt, i.e., Lactobacillus bulgaricus and Streptococcus thermophilus, may affect the necrosis of staphylococci in the product.…”