Different lactic acid bacteria are able to produce bacteriocins, proteinaceous substances with bactericidal activity against microorganisms closely related to the producer strain (64-67). Lactic acid bacteria are generally regarded as safe microorganisms and so are their bacteriocins. Thus, these bacteriocins can potentially be used to control the growth of spoilage and pathogenic organisms in food (68). Bacteriocin-producing lactococcal strains have been used successfully in starter cultures for cheese-making in order to improve the safety and quality of the cheese (69-71). For instance, the use of nisin-producing starter cultures was found to effectively reduce the spoilage by Clostridium tyrobutyricum strains (Fig. 4).
Recently it was found that the production of bacteriocins and bacteriocin-like compounds is a property that is very common among strains isolated from natural sources (15,16,72,73). This phenomenon can possibly be explained by the fact that the ability to produce antimicrobial compounds offers these wild strains the power to withstand the competition of other microorganisms and thus to survive in their hostile natural environment. The bacteriocin-producing wild lactococcal strains may be useful as starters in cheese making, not only because of their antimicrobial activity but also because of their potential to synthesize interesting flavor compounds (see below). These strains should then be combined with other strains that are bacteriocin-resistant.
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