The potential antimicrobial properties of tannins from Phyllanthus columnaris stem bark were evaluated against three Gram-positive cariogenic bacteria (Streptococcus salivarius ATCC 13419, Streptococcus oralis ATCC 6249 and Streptococcus mutans ATCC 25175), two obligate anaerobic Gram-negative periodontopathic bacteria (Porphyromonas gingivalis ATCC 33277, and Fusobacterium spp ATCC 25586), and five Candida spp (C. albicans ATCC 14053, C. parapsilosis ATCC 22019, C. tropicalis ATCC 750, C. krusei ATCC 6258 and C. glabrata ATCC 2001). Antimicrobial activities of tannins were determined using the disc diffusion test as well as minimum inhibitory concentration and minimum bactericidal/fungicidal concentration tests. The chemical composition of tannins was analysed by direct infuse mass spectrometry. Tannins inhibited the growth of all tested pathogens at MIC value ranging from 0.16 to 1.25 mg/mL. All tested bacteria showed similar higher level of susceptibility against tannins as the lowest MIC value was detected (0.16 mg/mL) except for S. oralis (0.63 mg/mL). However, both Gram negative anaerobes recorded the lowest MBC value at 0.32 mg/mL as compared to the Gram positive cariogenic bacteria (2.5->5.0 mg/mL). DIMS analysis of precursor ions detected four compounds present in tannins namely punicafolin, (S)-Nerolidol 3-O-[a-L-Rhamnopyranosyl-(1->4)-a-L-rhamnopyranosyl-(1->2)-[4-(4-hydroxy-3 methoxycinnamoyl)-(E)-a-L-rhamnopyranosyl-(1->6)]-b-D-glucopyranoside], ent-Epicatechin-(4alpha->8)-ent-epicatechin-(4alpha->8)-ent-epicatechin 3',3''-digallate and pavetannin C1 respectively.

Background Probiotics can be described as live microorganism which when consumed in adequate amounts, it will confer health benefits to the host. The benefits arising from probiotics has been mostly shown on gut health. However, its function to oral health is still poorly investigated. The aim of this study was to isolate lactic acid bacteria (LAB) from local fermented food and to determine its antibacterial activity, in order to select candidate probiotic strains for preventing caries. Methods The probiotic strains were isolated from five local fermented food which are tapai ubi, tapai pulut, rebung, thosai and taucu. Ten-fold serial dilutions of the fermented food samples were made in sterile peptone water before plating on de Man Rogosa and Sharpe (MRS) agar. The pure cultures were then randomly picked and biochemically identified. Then, the antibacterial activity of LAB against Streptococcus mutans were assessed by using disk diffusion method. Results A total of 120 LAB were isolated from five different fermented foods. The morphology of the isolates were circular, convex, dull opaque white or translucent white. Gram-staining identification showed that the isolates were Gram-positive rods. Of the 120 LAB isolates, 6 strains displayed moderate to strong antibacterial activity against S. mutans with the inhibition zones ranging from 7-12 mm. Conclusion The antibacterial activity demonstrated from LAB isolated from local fermented foods suggests that the isolates from local fermented foods possess antibacterial properties against pathogen responsible for causing dental caries. These strains are currently investigated in depth to assess whether they can be fully characterized as probiotics.