Apparent Antifungal Activity of Several Lactic Acid Bacteria against Penicillium discolor Is Due to Acetic Acid in the Medium

Abstract

Fifty-six dairy bacteria belonging to the genera Lactococcus, Lactobacillus, Pediococcus, Propionibacterium, Streptococcus, Enterococcus, Leuconostoc, and Brevibacterium were screened for antifungal activity against four species of fungi relevant to the cheese industry (Penicillium discolor, Penicillium commune, Penicillium roqueforti, and Aspergillus vesicolor). Most of the active strains belonged to the genus Lactobacillus, whereas Penicillium discolor was found to be the most sensitive of the four fungi investigated. Further studies on P. discolor showed antifungal activity only below pH 5. This effect of pH suggests that organic acids present in the culture could be involved in the detected activity. Determination of acid composition revealed lactic acid production for active dairy strains and the presence of acetic acid in active as well as inactive strains. It was demonstrated that the undissociated acetic acid originates from the bacterial growth medium. The synergistic effect of the acetic acid present and the lactic acid produced was likely the main factor responsible for the antifungal properties of the selected bacteria. These results could explain some discrepancies in reports of the antifungal properties of lactic acid bacteria, since the role of acetic acid has not been considered in previous studies.

The Use and Effects of Lactic Acid Bacteria in Malting and Brewing with Their Relationships to Antifungal Activity, Mycotoxins and Gushing: A Review

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Enhancing the Microbiological Stability of Malt and Beer - A Review

“…The antifungal activity of a sourdough isolate Lactobacillus sanfrancisco was due to mixtures of organic acids 33 . However, sodium acetate, a component of the growth medium for LAB was shown to have synergistic antifungal effects 21,190 .…”

Partial purification of an antifungal protein produced byEnterococcus faecalis CHD 28.3

“…Recently, a number of antifungal metabolites, e.g. cyclic dipeptides, phenyllactic acid, proteinaceous compounds, and 3-hydroxylated fatty acids have been isolated from Lactobacillus plantarum (Cabo et al, 2002;Lavermicocca et al, 2003;Schnürer and Magnusson, 2005).…”