Screening of novel compounds for inhibiting bacteria involved in dental caries

Dental caries is the most common infectious disease affecting humans. The main causative agents of this disease are bacteria especially group of streptococcal species. This study has examined the potential of using essential oils/antioxidants to control the growth of Streptococcus mutans and Streptococcus oralis in vitro in tryptone soya broth and a saliva medium in the presence and absence of sodium fluoride. A total of 9 essential oils and three antioxidants were screened using a clearing zone method. This showed that two essential oils (clove leaf, and cinnamon oils) and two antioxidants (butyl hydroxy anisole and propyl gallate) were the most effective. These were then tested at up to 10% concentration for inhibition of cell viability of both S.mutans and S.oralis. The ED50 and ED90 concentrations of these four compounds were determined. Studies were then carried out to examine the potential of integrating these compounds with sodium fluoride for inhibition of these two oral bacteria. Concentrations of 0.5 and 1% of the essential oils/antioxidants + 2000ppm sodium fluoride was able to completely inhibit growth of populations of both bacteria in TSB medium. Studies in an artificial saliva medium showed that these mixture were still effective resulting in >75% decrease in populations after treatment for 24 hrs. Ecological studies using the Bioscreen system showed that S.mutans and S.oralis could grow well at pH 5-7, but much more slowly at pH 4 as indicated by the times to detection and the increase in lag times prior to growth initiation. An increase in NaCl concentration from 1 to 6% (=0.999 to 0.97 water activity) showed a similar result for both bacteria.