Lactobacillus salivarius and L. gasseri down-regulate Aggregatibacter actinomycetemcomitans exotoxins expression

Abstract

Beneficial microbes, such as lactobacilli establish a symbiosis with the host and confer health-associated effects, by limiting the growth of indigenous pathogens and challenging microbes introduced by altered foods. Nevertheless, there is scarce information on the effects of beneficial microbes on the virulence properties of bacterial species associated with oral diseases, such as periodontitis. <i>Aggregatibacter actinomycetemcomitans</i> is a Gram-negative species highly implicated in the etiology of localized aggressive periodontitis. The objective of this study was to investigate the effect of lactobacilli on the expression of the two major virulence factors of <i>A. actinomycetemcomitans</i>. <i>Lactobacillus salivarius</i> and <i>L. gasseri</i> were selected as beneficial species. The gene expressions of leukotoxin (<i>LtxA</i>) and cytolethal distending toxin (<i>CdtB</i>) by <i>A. actinomycetemcomitans</i> were analyzed in response to challenge by lactobacilli cell-free supernatants. Neither lactobacilli affected the growth, but strongly attenuated the expressions of both <i>CdtB</i> and <i>LtxA</i> in the two <i>A. actinomycetemcomitans</i> strains tested. This reduction of the expression of these two exotoxins was time-dependent. These fundamental findings may indicate that lactobacilli can reduce the virulence of putative opportunistic oral pathogens, and may provide insights to future therapeutic approaches for the respective diseases.