[Influence of environmental factors on the two-species biofilm formed by Streptococcus oligofermentans and Streptococcus mutans ].

Objective To study the influence of environmental factors on the two-species biofilm formed by the combinations of Streptococcus oligofermentans (So) with Streptococcus mutans (Sm) and Streptococcus sanguinis (Ss) with Sm so as to evaluate the role of So in maintaining the microecological balance of the oral cavity. Methods Single-and two-species biofilms were grown on saliva-coated surfaces (glass tube and 96-well plate). Colony-counting method and safranin staining method were used to measure the biofilms formed under various oxygen conditions (aerobic and anaerobic), sucrose conditions (0%, 1% and 5% sucrose concentrations) and pH conditions (5.5, 6.0, 6.5, 7.0, 7.5 and 8.0). Results Comparing the numbers of Sm in two co-cultures under various conditions, Sm counts in So+Sm group [(7.70±2.46)×108 CFU/ml] were significantly lower than those in Ss+Sm group [(9.00±1.13)×108 CFU/ml] in aerobic environment (P<0.05). Sm counts in So+Sm group [(2.80±0.52)×108 CFU/ml] were also significantly lower than those in the Ss+Sm group [(4.00±1.25)×108 CFU/ml] in anaerobic environment (P<0.05). The Sm counts in So+Sm group [(8.90±0.82)×108 CFU/ml] were significantly higher than those in Ss+Sm group [(7.50±1.73)×108 CFU/ml] in 0% sucrose environment (P<0.05). The Sm counts in So+Sm group [(5.70±2.94)×108 CFU/ml] were significantly lower than those in Ss+Sm group [(10.30±3.21) ×108 CFU/ml] in 1% sucrose environment (P<0.05). The Sm counts in So+Sm group [(6.10±1.71)×108 CFU/ml] were also significantly lower than those in Ss+Sm group [(7.40±1.20)×108 CFU/ml] in 5% sucrose environment (P<0.05). The Sm counts in So+Sm group [(3.50±1.50)×108 CFU/ml] were significantly lower than those in Ss+Sm group [(10.70±2.80)×108 CFU/ml] in pH7.0 environment (P<0.05). Comparing the formation of biofilm after 24 h cultivation, the Sm counts in So+Sm group were significantly lower than those in Ss+Sm group both in aerobic and anaerobic environments (P<0.05). The Sm counts in So+Sm group were significantly higher than those in Ss+Sm group in 0% sucrose environment (P<0.05). The Sm counts in So+Sm group were significantly lower than those in Ss+Sm group in 1% and 5% sucrose and pH 7.0 environments (P<0.05). Both So and Ss had no inhibitory effect on Sm in pH5.5 and pH8.0 environments. Conclusions In the in vitro two-species co-culture systems, So showed stronger inhibitory effects than Ss on Sm and its inhibitory ability might influenced by various environmental factors. Key words: Streptococcus mutans; Streptococcus sanguinis; Streptococcus oligofermentans; Oxygen; Sucrose; pH values