EFFECT OF LACTOBACILLUS-RHAMNOSUS STRAIN GG (ATCC-53103) ON THE GROWTH OF STREPTOCOCCUS-SOBRINUS IN-VITRO

Lactobacillus GG, a recently characterized L. rhamnosus GG strain (ATC C 53103), has been shown to exert inhibitory activity against a variet y of bacterial species, including streptococci. We isolated and studie d the effect of the inhibitory substance of Lactobacillus GG on some o ral streptococci. The inhibitory activity of the isolated substance wa s weak, but some growth inhibition was observed in Streptococcus sobri nus pretreated with the substance in comparison with untreated control s. Zones of growth inhibition on agar plates were apparent only at pH values below 5, indicating that the inhibitory activity was restricted to a low pH range. Growth curve experiments showed a statistically si gnificant inhibition between series with and without the isolated subs tance (P < 0.05). The ultrastructure of S. sobrinus was not affected w hen treated with the inhibitory substance. The Lactobacillus GG itself did not ferment sucrose. The results offer interesting perspectives f or future research focusing on the protective function of normal flora and in the attempt to replace harmful bacterial species in oral micro flora with less harmful ones.