Nutritional Factors Affecting Growth and Production of Antimicrobial Substances by Streptococcus lactis subsp. diacetylactis S1-67/C

Antifungal attributes of lactic acid bacteria--a review

Molds constitute a very important contaminating flora of dairy products. Contamination with undesirable molds has been a serious and frequently disturbing problem in the dairy industry that results in huge losses due to spoilage of cheese and other fermented foods incriminated by a variety of mycoflora such as Aspergillus, Penicillium, Fusarium, Rhizopus, and Mucor. The considerable drop in pH caused by the growth of lactic acid bacteria (LAB) in fermented milk makes such foods a breeding ground for the highly opportunistic fungi to proliferate and thrive, spoiling the products and effecting cost and its commensurate accessories. The major antimicrobial substances isolated from the LAB are found effective against bacteria only and their inhibition toward the growth of contaminating bacteria has been explored in detail. However, studies on the fungistatic properties of LAB are relatively rare. This article reviews the investigative studies on the antifungal aspects of different lactic acid bacteria and the prospects of this exceptional trait as a potential food biopreservative.

Production of antifungal substance by Lactococcus lactis subsp. lactis CHD-28.3

Six of the 2100 colonies of lactic acid bacteria isolated from 4 month old Cheddar cheese and raw buffalo milk showed antifungal activity against Aspergillus flavus IARI when tested by the well agar diffusion assay on Potato Dextrose Agar containing 0.1% Triton X-100. Out of these, the most promising isolate having a broad spectrum of antifungal activity including Aspergillus flavus IARI, A. flavus NCIM 555, A. parasiticus NCIM 898 and Fusarium spp. was identified as Lactococcus lactis subsp. lactis CHD-28.3. Among the mold cultures used as indicator strains, the most sensitive towards antifungal substance produced by the test culture was A. flavus IARI. The cell-free supernatant of the test culture in Elliker's broth adjusted to pH 6.8 produced an inhibition zone of 15-19 mm against A. flavus IARI, A. flavus NCIM555 and A. parasiticus NCIM898. The isolate when grown at 30 degrees C for 48 h in Elliker's broth showed optimum antifungal activity. When the supernatant was neutralized to pH 7.0 or 7.5, there was little reduction in activity. However, after enzymatic treatment of supernatant with chymotrypsin, trypsin and pronase E, the antifungal activity disappeared which indicated the proteinaceous nature of the antifungal substance.

Sakacin M, a bacteriocin-like substance from Lactobacillus sake 148

The antagonistic activity of Lactobacillus sake 148 was evaluated during its growth on complex broth media and in a semisynthetic defined medium (SDM) with various supplements. The antagonistic activity was a growth-associated property, being detected and quantified when L. sake 148 was grown at either 4, 8, 16, 25 or 32 degrees C. The concentrated culture supernatant of L. sake 148 was subjected to purification by lyophilization and gel filtration. The purification procedure resulted in a small increase in its specific activity (7-fold) and in a low recovery of the original inhibitory activity (8%). Gel filtration analysis of the partially purified activity on Sephadex G-50 revealed an apparent molecular weight of 4640. The partially purified antagonistic activity of L. sake 148 was destroyed by treatment with proteolytic enzymes. However, the antagonistic activity was resistant to heat, having D-values at 121, 135 and 150 degrees C of 23.8, 17.4 and 15.2 min, respectively.