In vitro antibacterial effect of fifth generation dentin bonding agent incorporated with nisin on Streptococcus mutans

Bacterial adherence to restorative materials such as composite resin is one of the aetiology of secondary caries. This study evaluated the antibacterial efficacy of fifth generation bonding agent (BA) modified with nisin, against Streptococcus mutans based on its growth, adherence and membrane integrity.

Adhesive eluents of the experimental bonding agents were obtained using 250?μl Brain Heart Infusion (BHI) broth and the groups were control (BA with 0% Nisin), bonding agent with 1 wt% (NBA 1) and 5 wt% nisin (NBA 5). To this, 10?μl S. mutans culture was added and incubated at 37?°C. Bacterial growth was estimated by changes in optical density using spectrophotometer every 20?min for 2?h. The results were statistically analysed using one way ANOVA followed by Tukey Post Hoc test. For adherence and membrane integrity test, 10?μl of BHI supplemented with 1% sucrose and 50?μl of bacterial suspension were inoculated onto the cured specimens, and incubated for 4?h. After rinsing, 1?ml of Live/Dead BacLight bacterial viability stain was added and incubated in the dark for 15?min and observed under confocal laser scanning microscope (CLSM) for intact (green/live) and damaged (red/dead) bacterial membranes.

Mean optical density was significantly higher in control group at all time intervals with maximum value at 2?h (0.83?±?0.008), while there was a concentration dependant reduction in bacterial growth with the NBA groups (0.50?±?0.007). Correspondingly, the NBA groups showed higher amount of dead than live bacteria, while live bacteria were predominant in the control group.

Addition of an antibacterial agent nisin in dentin bonding agent may render the resin dentin interface more resistant to bacterial penetration, and adherence of cariogenic bacteria like S. mutans.