Material and Methods: 1. Confocal laser scanning microscope (CLSM) analysis- S. mutans UA159 and luxS deficient mutant (TW26) were grown as biofilm in the presence of synthetic AI-2 (DPD). The ratio of live/dead bacteria in biofilm was analyzed using CLSM.
2. FTF immunoblotting analysis- S. mutans UA159 and TW26 were grown as planktonic cultures and biofilm in the presence of DPD. Spent media and cells lysates were blotted and FTF expression was analyzed using anti-FTF antibodies and labeled secondary antibodies.
Results: 1. CLSM analysis- Amounts of total bacteria were 1.5-2 folds higher in samples of S. mutans UA159 and TW26 exposed to DPD in comparison with control samples. Dead bacteria were 5-10 folds lower in samples of UA159 exposed to DPD in comparison with same treatment in TW26.
2. FTF immunoblotting analysis- at logarithmic growth stages, intra-cellular FTF increased more then two folds when exposed to DPD, in compare with control samples. The increment was smaller in bacteria at stationary phase and biofilm. In S. mutans TW26, intra-cellular FTF synthesis was not changed.
FTF secretion was reduced in TW26 at logarithmic growth stages in compare with wild type. The presence of DPD had almost no effect on FTF secretion in both strains.
Conclusions: 1. DPD can contribute to bacterial vitality in S. mutans UA159 and TW26 biofilm, while the existence of the luxS gene can increase the ratio between live and dead bacteria within the biofilm.
2. DPD increases FTF synthesis especially at the early growth stages but only in the presence of the luxS gene. DPD doesn't influence FTF secretion while deletion of the luxS gene decreases FTF secretion, especially at early bacterial growth stages.