Methods: In this study, L. casei Shirota was isolated from a popular probiotic drink (Yakult®). The biofilms of mono-culture and co-culture of S. mutans ATCC25175 and L. casei Shirota in brain heart infusion (BHI) with 1% sucrose were carried out on a 24 well microplate for 24 hours. The biofilms were assessed by crystal violet staining. The 24h mono-culture and co-culture biofilms were also formed on glass cover slips. The biofilms were washed, harvested and plated on selective agar plates after serial dilution. The bacteria adherence was quantified using the number of colony-forming units (CFU). Scanning electron microscopy (SEM) was employed to visualize the biofilm architecture. The data were analyzed using t-test (SPSS19.0).
Results: S. mutans formed a distinct biofilm, while L. casei Shirota hardly colonized on glass cover slip. Adherence of S. mutans in co-culture biofilm (7.28±0.04 LogCFU/ml) was as same as that in mono-culture biofilm (7.38±0.28 LogCFU/ml) (p>0.05). However, adherence of L. casei Shirota (7.48±0.08 LogCFU/ml) was significantly higher than that in mono-culture biofilm (4.84±0.08 LogCFU/ml) (p<0.01). By SEM observation, co-culture biofilm demonstrated loose architecture in comparison with S. mutans mono-culture biofilm.
Conclusions: L. casei Shirota affected S. mutans biofilm architecture; however, it had no significant effect on S. mutans adherence. On the contrary, S. mutans enhanced L. casei Shirota adherence. These findings provided a possible mechanism for the potential cariostatic effect of probiotic drink.