Acid production rate of streptococcus mutans after adaptation in human breast milk

Abstract

Objective: This study aims to investigate an adaptation of acid production of S. mutans to long-term exposure to human breast milk (HBM).

Materials and Methods: S. mutans UA 159 were grown in pooled HBM from 11 mothers. To create the adaptation condition, S. mutans were sub-cultured up to the 15th passage (11 hours/passage) in HBM, BHI supplemented HBM (HBM+BHI) and BHI control. The bacterial cells were collected at the baseline (the 0 passage), the 1st, 5th, 9th, 13th and 15th passage to immediately determine the acid production and growth in HBM and 7% sucrose supplemented BHI (BHI+Sucrose). The pH and the number of bacteria were measured every hour for 6 hours and after 12 hours of incubation. The acid production rate was calculated at the fastest pH-dropping duration.

Results: The acid production in HBM and in BHI+Sucrose of S. mutans was changed after exposure to all three media for 11 hours (the 1 passage). The acid production in HBM of HBM and HBM+BHI grown cells reached the critical pH of enamel after 2-3 hours which was faster than the baseline HBM (4 hours). The acid production rate in HBM and in BHI+Sucrose of all tested group was not significant difference. Moreover, the longer period of exposure was performed; there was not obvious discrepancy of acid production among the 1st through the 15th passage.

Conclusion: After exposure to HBM, S. mutans increase its ability to utilize HBM leading to the shorter time to reach critical pH than its usual condition.