The viridans group streptococci (VGS) have been used as probiotic bacteria in upper respiratory tract infections due to their good interfering activity against Group A streptococci (GAS) and S.pneumoniae. Lactobacilli have also been discussed in this regard.
The aim of the study was to see if the interfering activity of selected clinical and commercial strains of Lactobacilli could inhibit the growth of GAS strains in vitro.
Different commercial lactobacilli strains were tested. As commensal bacteria, clinical isolates of VGS (S. oralis and S. sanguinis) were used. Both the agar overlay method and the PBS supernatant method were employed under different pH conditions
Results: Of the tested commercial strains, Lactobacillus plantarum LB931 and Lactobacillus rhamnosus LB21 most effectively inhibited GAS. However, they were not as competent as S.oralis and S.sanguinis, both being very good inhibitors. Together, lactobacilli and commensal VGA strains produced the fastest and most effective killing of the GAS.
Conclusion: Some lactobacilli strains had an interfering effect on GAS. Together with commensal bacteria as VGA, an improved growth inhibitory effect could be seen. We also found that the pH is important when testing bacterial interference in vitro.
We suggest that the efficacy of probiotic strains of Lactobacilli in eradicating GAS should be further investigated in clinical studies.