Anticandidal Activities by Lactobacillus Species: An Update on Mechanisms of Action

Abstract

Lactobacilli are among the most studied bacteria in the microbiome of the orodigestive and genitourinary tracts. As probiotics, lactobacilli may provide various benefits to the host. These benefits include regulating the composition of the resident microbiota, preventing - or even potentially reverting- a dysbiotic state. Candida albicans is an opportunistic pathogen that can influence and be influenced by other members of the mucosal microbiota and, under immune-compromising conditions, can cause disease. Lactobacillus and Candida species can colonize the same mucosal sites; however, certain Lactobacillus species display antifungal activities that can contribute to low Candida burdens and prevent fungal infection. Lactobacilli can produce metabolites with direct anticandidal function or enhance the host defense mechanisms against fungi. Most of the Lactobacillus spp. anticandidal mechanisms of action remain underexplored. This work aims to comprehensively review and provide an update on the current knowledge regarding these anticandidal mechanisms.

Keywords: Candida; Lactobacillus; candidiasis; dysbiosis; microbiome; microbiota; probiotics.

Figure 1

Direct antifungal modes of action. Lactobacillus species produce diverse metabolites including bacteriocins, enzymes (chitinases), hydrogen peroxide, fatty and other organic acids, as well as proteinaceous molecules (reuterin), that exert direct anticandidal activity via different mechanisms of action. Some metabolites alter the physiology of the fungus by inducing oxidative stress or by ATP depletion leading to cytotoxicity or growth inhibition. Other metabolites compromise the structural integrity of the fungal cell leading to alterations in cell morphology, membrane permeability, and death, while biosurfactants prevent adhesion to mucosal surfaces.

Figure 2

Indirect antifungal modes of action. Lactobacillus interacts with the host to stimulate protective, antifungal functions. These mainly result from competition with Candida in binding to mucus membrane glycoconjugates; strengthening the mucosal barrier through induction of mucins and positive regulation of tight junction proteins; activation of T and B cell immune responses; downregulation of host-destructive inflammation; and induction of innate epithelial antimicrobial peptides.