Antimicrobial Substances Produced by Lactic Acid Bacteria

ANTIMICROBIAL SUBSTANCES PRODUCED BY LACTIC ACID BACTERIA 

LAB are non-respiring microorganisms, principally generating ATP by fermentation of carbohydrates coupled to substrate-level phosphorylation. The two major pathways for the metabolism of hexoses are homofermentative or glycolysis (Embden-Meyerhof pathway), in which lactic acid is virtually the only end-product, and heterofermentative (phosphoketolase pathway), in which other end-products such as acetic acid, C02, and ethanol are produced in addition to lactic acid (Axelsson et al., 1989 Kandler, 1983 Zourari et al., 1992). 

Of the two major weak organic acids produced by LAB (acetic and lactic acid), acetic acid is the strongest inhibitor because of its higher dissociation constant (pKa = 4.75) as compared to lactic acid (pKa = 3.08) at a given molar concentration and pH level (Eklund, 1983 Holzapfel et al., 1995 Ouwehand, 1998). 

Reuterin is a neutral broad-spectrum antimicrobial substance formed during anaerobic growth of Lactobacillus reuteri in the presence of glycerol (Axelsson et al., 1989). Reuterin is an equilibrium mixture of monomeric, hydrated monomeric, and cyclic dimeric forms of (Vhydroxypropionalde-hyde. The inhibitory effect of reuterin has been associated with its action on DNA synthesis by acting as an inhibitor of the substrate binding subunit of ribonucleotide reductase. 

Ouwehand, 1998). In cases in which the mode of action has been investigated, the cell membrane appears to be the site of action. There is enough evidence to conclude that bacteriocins produced by LAB act by the common mechanism of depleting proton motive force (PMF) (Bruno et al., 1992). 

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III. Antimicrobial Substances Produced by Lactic Acid Bacteria... 

III. ANTIMICROBIAL SUBSTANCES PRODUCED BY LACTIC ACID BACTERIA... 

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