In Vitro Inhibitory Effect of Two Probiotics on Chromogenic Actinomycetes

Objectives:
New strategies to prevent oral diseases are based on manipulating oral microbiota, which is provided by probiotics.
The aim of this study was to evaluate the effects of two commercially available probiotics Streptococcus salivarius M18 and Lactobacillus reuteri Prodentis on growth inhibition of chromogenic bacteria, specifically A. actinomycetemcomitans and A. naeslundii.
Methods: this in vitro study was carried out using their cell-free fermentative broth in a planktonic growth inhibition test.
Streptococcus salivarius M18 and Lactobacillus reuteri for each of the strains were used as probiotic strains. Two types of oral bacteria were used to test the antibacterial effect of these probiotic strains Aggregatibacter actinomycetemcomitans and Actinomyces naeslundii
They were cultured using Schaedler agar with vitamin K and 5% Sheep Blood in anaerobic conditions.
Results:
Anti-A. actinomycetemcomitans activity of S. salivarius M18 occurred at a concentration of 40% (Figure 1a), with a complete growth inhibition at 90% (Figure 1a), while anti –A. naeslundii activity of S. salivarius occurred at a concentration of 60% with a complete growth inhibition at 90% (Figure 1b), demonstrating that A. actinomycetemcomitans is more susceptible to the antimicrobial activity of S. salivarius than A. naeslundii.
Anti-A. actinomycetemcomitans activity of L. reuteri occurred at a concentration of 60% (Figure 2a), with a complete growth inhibition at 90% (Figure 2a), while anti –A. naeslundii activity of L. reuteri occurred at a concentration of 90% without reaching a complete growth inhibition at this concentration (Figure 2b), demonstrating that A. actinomycetemcomitans is more susceptible to the antimicrobial activity of L. reuteri than A. naeslundii.
Conclusions: These data show that Actinomyces naeslundi is less susceptible to the probiotic activity of both S. salivarius and L. reuteri. However, Streptococcus salivarius showed a stronger antimicrobial activity than Lactobacillus reuteri against the two indicator strains used.