Synergism Between Streptococcus Mutans and Candida Albicans Against Oxidative Stress
Objectives: Candida albicans and Streptococcus mutans display a synergistic association that promotes dental caries. The enhancement of production of extracellular matrix when S. mutans and C. albicans are co-cultured is thought to contribute to virulence and tolerance to environmental insults. The purpose of the study is to explore the role of extracellular matrix and C. albicans catalase in the protection against oxidative stress in a dual species biofilm model of S. mutans and C. albicans.
Methods: C. albicans SC5314 and its derivative catalase mutant were co-cultivated with S. mutans UA159 or its derivative glucosyltranferase B/C mutant. Single species and the dual species groups in different combinations were allowed to grow as biofilms on hydroxyapatite discs in TYES media. After 48 hours, a lethal dose of 0.25% H2O2 was added to the biofilms and incubated for 30, 60, and 90 minutes. The biofilms were removed from the discs through sonication. Serial dilution plating was performed, plates were incubated at 37°C for 48 hours and CFUs were quantified to calculate survival rates.
Results: Survival rate of S. mutans in a dual species biofilm in the presence of C. albicans SC5314 was greater than the survival rate of S. mutans co-cultivated with the C. albicans catalase mutant or when grown as a mono species biofilm (p≤ 0.05). In addition, the C. albicans catalase mutant was hypersensitive to H2O2 challenge (p≤ 0.05). Inactivation of glucosyltransferase B/C in S. mutans did not affect the survival rate of S. mutans in dual species or mono species biofilms.
Conclusions: Our data suggests that catalase produced by C. albicans protects S. mutans against H2O2. Production of robust extracellular matrix does not appear to play major role in protection of S. mutans or C. albicans against oxidative stress.