RESUMEN
The gum of Cratoxylum formosum, commonly known as mempat, is a natural agent that has been used extensively for caries prevention by hill tribe people residing in Thailand. The objective of this study was to investigate the antimicrobial activity of Cratoxylum formosum gum on Streptococcus mutans (S. mutans) in vitro. The gum extracted from stem bark of Cratoxylum formosum was investigated for antimicrobial activity against different strains of S. mutans, including S. mutans KPSK2 and 2 clinical isolates. Inhibition of growth was primarily tested by agar diffusion method. A two-fold broth dilution method was then used to determine the minimum inhibitory concentration (MIC) of the extract. The extract of Cratoxylum formosum was effective against S. mutans with the inhibition zones ranging from 9.5 to 11.5 mm and MIC values between 48 microg/ml and 97 microg/ml. The gum of Cratoxylum formosum has high antimicrobial activity against S. mutans and may become a promising herbal varnish against caries.