Production of antimicrobial substances by lactic acid bacteria II: screening bacteriocin-producing strains with probiotic purposes and characterization of a Lactobacillus bacteriocin.

Bacteriocins have been defined as proteinaceous, bactericidal substances synthesized by bacteria, which usually have a narrow spectrum of activity, only inhibiting strains of the same or closely related species. The term bacteriocin-like substance is applied to antagonistic substances that are not completely defined or do not fit the typical criteria of bacteriocins. They have been reported to inhibit a wide range of both Gram-positive and Gram-negative bacteria as well as fungi. Lactobacillus species are the dominant microorganisms isolated from the vagina of healthy premenopausal women. In this environment, they exert a protective effect against pathogenic microorganisms by different mechanisms such as production of antimicrobial agents, which include organic acids, hydrogen peroxide, and probably bacteriocins. The production of bacteriocins by vaginal lactobacilli has been demonstrated in vitro; however, it is not yet well established whether they are produced in vivo as another antagonistic mechanism exerted by the normal microflora.Bacteriocin-producing bacteria as well as bacteriocins per se are of growing interest as biological controls in the manufacture of beverages and fermented products, mainly in the area of dairy products. These bacteria have also been proposed as probiotic candidates for human or animal use. The objectives of the present chapter are to describe the methods employed for: 1. Detection of production of bacteriocins among vaginal Lactobacillus strains. 2. Characterization of the bacteriocin or bacteriocin-like substances. 3. Study of the kinetics of production and mode of action of bacteriocins. 4. Determination of the inhibition of pathogenic microorganisms by bacteriocin-producing strains in mixed cultures.