Purpose. Lactobacillus reuteri, a species used in probiotic products, produces in vitro a bacteriocin, reuterin, in the presence of glycerol. The purpose of the study was to investigate in vitro whether L. reuteri strains inhibit the growth of periodontal pathogens.
Methods. The inhibition study was based on a disk-diffusion method. The periodontitis-associated bacteria were pre-grown for 20 h in Brucella broth or Brucella blood agar at 37oC in anaerobic atmosphere. Standardization of bacterial inocula used in the assay was made by determinations of optical density, microscopic counting of cells, and viable count. Brucella blood agar plates, without or with glycerol (100 mM), were seeded with standardized inocula of the periodontal pathogens Fusobacterium nucleatum (IDH 4186), Porphyromonas gingivalis (ATCC 33277), Prevotella intermedia (ATCC 25611), and Actinobacillus actinomycetemcomitans (SA 1398). The lactobacilli L. reuteri ATCC 55730 and L. reuteri PTA 5289 were grown for 16 h in MRS broth. A 20-L aliquot of the suspension containing 107 CFU/mL was used to soak 6-mm paper disks, which were placed on Brucella agar plates (diameter 14 cm), seeded with each periodontal pathogen separately. The plates were then incubated for 3 - 7 days in anaerobic atmosphere at 37oC before measuring the inhibition zones.
Results. On Brucella blood agar plates seeded with periodontal pathogens, no inhibition zones were seen around the paper discs. When glycerol was added to the agar, zones of 26 to 118 mm appeared. Sizes of the zones depended on the L. reuteri strain, the periodontal pathogen, and the sizes of their inocula. L. reuteri PTA 5289 had a stronger (7-30%) inhibitory effect than L. reuteri ATCC 55730 on all periodontal species. P. gingivalis was the most susceptible species among the tested strains.
Conclusion. Both L. reuteri strains strongly inhibited or suppressed the growth of the tested periodontitis-associated bacteria in the presence of glycerol. The inhibitory activity of L. reuteri PTA 5289 was consistently higher than that of L. reuteri ATCC 55730. The results suggest that the inhibition activity of the tested lactobacilli was related to reuterin.