Antibacterial Activity of Thai Medicinal Plant Extracts Against Oral and Gastrointestinal Pathogenic Bacteria and Prebiotic Effect on the Growth of Lactobacillus acidophilus

Abstract

The 25 crude methanolic extracts of Thai medicinal plants were tested for their antibacterial activity against 10 bacterial strains using disk diffusion assay and minimum inhibitory concentration (MIC) determination. Rhubarb (Rheum palmatum) root, wild turmeric (Curcuma aromatica) rhizome, aleppo oak (Quercus infectoria) gall and ringworm bush (Cassia alata) stem extracts possessed strong antibacterial activity. Aleppo oak and wild turmeric extracts strongly inhibited Y. enterocolitica growth, while aromatic ginger (Kaempferia galanga) rhizome, rhubarb, wild turmeric and ringworm bush extracts strongly inhibited the growth of Porphyromonas gingivalis, an oral pathogen (0.32 mg/mL MIC). The aleppo oak gall extract had the highest phenolics and tannins (672.13 mg gallic acid equivalents (GAE)/g extract and 884.79 mg tannic acid equivalents (TAE)/g extract, respectively), whereas copper pod (Peltophorum pterocarpum) stem bark extract had the highest flavonoids (5,293.60 mg quercetin eqivalents (QE)/g extract). Five plant extracts with high water soluble carbohydrate were tested for their prebiotic properties. Their indigestible polysaccharide contents and prebiotic effect on the growth of Lactobacillus acidophilus in MRS broth were determined. Of all, mangosteen (Garcinia mangostana) fruit peel, nutgrass (Cyperus rotundus) rhizome and gac (Momordica cochinchinensis) root extracts had high indigestible polysaccharide contents, and exhibited good stimulating effect to the growth of L. acidophilus.