Biofilms of Candida albicans and Streptococcus sanguinis and their susceptibility to antimicrobial effects of photodynamic inactivation.

This study evaluated the effects of photodynamic inactivation (PDI) on single and multi-species biofilms, compounds by Candida albicans and Streptococcus sanguinis. Biofilms were formed, on microplate of 96 wells, by suspensions of C. albicans (ATCC 18804) and S. sanguinis (ATCC 7073) adjusted in 107 cells/mL, followed by incubation of 48 h (with 5% CO2). The effects of the photosensitizer erythrosine (ER) at 400 µM for 5 min and green light-emitting diode (LED - 532 ±â€¯10 nm) for 3 min, alone and conjugated, were evaluated. After normality test, results was analysed by Tukey´s test (P < 0.05). PDI group promoted reductions of 1.07 and 0.39 log10, respectively, in biofilms of C. albicans alone and in association with S. sanguinis. Biofilms of S. sanguinis alone were more sensitive, with reduction of 4.48 log10. When in association with the yeast, S. sanguinis have a decrease of 2.67 log10. SEM analysis revealed a decrease in bacterial and fungal structures of biofilms treated with PDI. In conclusion PDI promoted significant microbial reductions in both species of microorganisms grown on mixed biofilms. This study is one of the pioneers to evaluate the antimicrobial action of PDI on biofilms of S. sanguinis and C. albicans, demonstrating a way to control these microorganisms of clinical importance.

Influence of sucrose on growth and sensitivity of Candida albicans alone and in combination with Enterococcus faecalis and Streptococcus mutans to photodynamic therapy.

This study has evaluated the effects of photodynamic inactivation (PDI) using erythrosine as photosensitizer and green light-emitting diode (LED) on biofilms of Candida albicans alone and in combination with Enterococcus faecalis and Streptococcus mutans. We have also evaluated the effect of sucrose on biofilm formation and bacterial growth and sensitivity to PDI. Biofilms were formed in suspension of 106 cells/ml on plates before being grown in broth culture with and without sucrose and incubated for 48 h. Next, the treatment was applied using erythrosine at a concentration of 400 µM for 5 min and green LED (532 ± 10 nm) for 3 min on biofilms alone and in combination. The plates were washed and sonicated to disperse the biofilms, and serial dilutions were carried and aliquots seeded in Sabouraud agar before incubation for 48 h. Next, the colony-forming units per milliliter (CFU/ml; log10) were counted and analyzed statistically (ANOVA, Tukey test, P ≤ 0.05). Results show that S. mutans favors the growth of C. albicans in biofilms with sucrose, with treatment not being effective. However, when the biofilm was grown without sucrose, we found a reduction in biofilm formation and a significant decrease in the PDI treatment (P < 0.0001). In conclusion, both growth and sensitivity to PDI in biofilms of C. albicans are strongly influenced by bacterial combination, and the presence of sucrose affected directly the growth and sensitivity of the biofilm to PDI as sucrose is the substrate for construction of the exopolysaccharide matrix.