Inhibitory Effect of Sodium Benzoate on the Growth of Cariogenic Micro-organisms

Objectives: Sodium Benzoate (NaB) is used as preservative in food and pharmaceutical products, based on its antimicrobial action that is pH sensitive. The present study aimed to determine the optimum concentration and pH at which NaB may exhibit adequate antibacterial effect as to inhibit or reduce the growth of S. mutans. Methods: Two experiments (A and B) were devised. In A, the pH of Brain Heart Infusion (BHI) broth with added 0.1% NaB was adjusted so as to produce nine experimental groups of varying pH; 5.25, 5.5, 5.75, 6.0, 6.25, 6.5, 6.75, 7.0 and 7.0-without-NaB (control). These were inoculated with S. mutans (NCTC 10449) and incubated aerobically at 37°C for 18 hours. Bacterial growth was assessed by determination of number of colony forming units per milliliter (cfu/ml) following serial 7-fold dilution, inoculation in BHI agar and aerobic incubation at 37°C. The pH at which the greatest growth inhibition was observed was determined. Keeping the pH of BHI broth at this pre-determined pH (5.25), the above experiment was repeated with the concentration of NaB in the broth adjusted to produce eight groups of varying %NaB; 0.0 (control), 0.05, 0.075, 0.1, 0.125, 0.15, 0.175 and 0.2%. Results: In A, paired-t test (a=0.05) indicated a significant (n=5, p<0.05) growth inhibition within pH 5.25 to 6.25 when compared with the control. The most significant (p<0.001) growth inhibition was observed at pH 5.25. No statistical significant inhibition was observed from pH 6.5 to 7.0 when compared with the control. In B, significant (n=5, p<0.05) growth inhibition was observed in all groups when compared with the control. This effect increased with increase concentration of NaB. Conclusion: Sodium benzoate markedly inhibited the growth of cariogenic bacteria (S. mutans) at 0.2% concentration and pH 5.25, highlighting its potential as an active ingredient in caries prophylactic oral rinse products.