Objective: Numerous pathogenic microorganisms are associated with oral inflammatory diseases such as gingivitis and periodontitis. Modifying the oral microflora via probiotic application may therefore be a useful mechanism for reducing these ailments. The objective of this study was to determine the effects of two commercially-available oral probiotics on pathogen-induced pro-inflammatory cytokine expression in gingival fibroblasts (GFs).
Methods: Human primary GFs were cultivated as adherent monolayers in 24 well plates. The monolayers were first challenged separately for 4 and 8 hours with periodontitis-associated Porphyromonas gingivalis 33277, Aggregatibacter actinomycetemcomitans Y4 and Fusobacterium nucleatum 10593, and oral probiotic strains Streptococcus salivarius K12 and M18 at a 25:1 multiplicity of infection (MOI). GFs were then challenged simultaneously with equal amounts of the pathogens and probiotics at the same MOI, with and without an additional probiotic pre-incubation step. Culture supernatants were collected and assessed for expression of IL-6 and IL-8 using Luminex bead-based technology. Analysis of variance with Bonferroni's post test was used to determine significance, assessed at p<0.05 (N=3).
Results: When applied separately or in combination to GF monolayers, all three pathogens significantly increased both IL-6 and IL-8 expression over control levels at 4 and 8 hours. In contrast, neither probiotic strain alone affected expression of either cytokine at either timepoint. When incubated alongside the pathogens, both probiotic strains were found to significantly inhibit the majority of this pathogen-induced cytokine upregulation, regardless of whether the monolayers were pre-incubated with the probiotics or not. The effects were far greater for IL-8, where all probiotic-pathogen combinations significantly reduced expression at both timepoints.
Conclusions: Commercially-available oral probiotic strains S. salivarius K12 and M18 were both able to downregulate the expression of cytokines associated with inflammatory conditions like gingivitis and periodontitis. Therefore, these strains may offer novel preventive and therapeutic options for patients suffering from both diseases.