Lactobacillus delbreuckii Produces An Antimicrobial Protein That Inhibits Porphyromonas gingivalis

Objectives: Despite a growing interest in using probiotic micro-organisms to prevent disease, very little is understood about the mechanisms by which probiotics exert their action. We are interested in understanding the interactions between Porphyromonas gingivalis (Pg), an important pathogen implicated in the development of periodontitis, and probiotic bacteria such as Lactobacillus.
Methods: We isolated several probiotic strains of Lactobacillus delbrueckii from dairy products and examined their ability to inhibit Pg growth in vitro. We employed agar overlays and spot plating to test for inhibition of Pg. We also utilized whole genome sequencing to compare strains of L. delbrueckii.
Results: We identified L. delbrueckii strains that inhibit Pg growth in vitro. There is strain specificity in the inhibition as some, but not all, strains of L. delbrueckii inhibit Pg growth. Whole genome sequencing of inhibitory and non-inhibitory strains of L. delbrueckii revealed significant genetic differences and the presence of additional genes with homology to inhibitory bacteriocins. Testing of L. delbrueckii supernatants and lysates to characterize the mechanism of inhibition suggest that the inhibitory molecule is a heat-labile, protease-sensitive protein with a molecular weight between 30-100 kDa. We have partially purified the inhibitory protein(s) from L. delbrueckii lysates using ammonium sulfate precipitation, anion exchange chromatography, and gel filtration chromatography. We have demonstrated that L. delbrueckii inhibitory lysate is bactericidal against stationary-phase Pg reducing Pg viability by approximately 10,000-fold over three hours.
Conclusions: Our results underscore the importance of strain selection, not simply species selection, in understanding microbial interactions. Specific L. delbrueckii strains or their products may be effective in the treatment and prevention of Pg-associated periodontal disease.