A study was carried out to isolate and identify the active compounds from Melastoma malabathricum stem bark that exhibit anti-biofilm and anti-adherence activities against Streptococcus mutans. Purification of the active compounds from the stem bark extract was performed via silica gel chromatography to produce 12 fractions. Further fractionation of fraction 9 by high performance liquid chromatography (HPLC) produced 21 sub fractions. All the sub fractions were subjected to thin layer chromatography (TLC) bioautography as preliminary screening to determine anti bacterial activity. TLC-bioautography showed that sub fraction 18 (SF18) demonstrated large inhibited zone against S. mutans. Gas chromatography mass spectrometry (GCMS) was used to identify the active compounds in SF18. Fraction SF18 revealed 27 compounds such as hexanoic acid, 8-methyl-1-undecene, propanenitrile, and 1-decene. Anti-biofilm and anti-adherence activities were determined using crystal violet and glass surface assays respectively. The concentrations that produced 50% reduction in anti-biofilm and anti-adherence activities were 1.88 mg/ml and 3.75 mg/ml respectively. � 2014 AIP Publishing LLC.

Streptococcus mutans is the earliest bacteria that forms dental caries in humans. This study determines the effect of acetone extract from Melastoma malabathricum stem against S. mutans by microscopic observation and absorption of fluorescence dye. The extraction of M. malabathricum stem using acetone yielded 0.5 g of acetone extract. Anti-bacterial activity determined by disk diffusion assay showed that stem extract at the 30 mg/mL inhibit bacterial growth with inhibition zone diameter of 15 mm. The effect of the extract towards S. mutans by microscopic observation was done by Scanning Electron Microscope (SEM) and Transmission Electronic Microscope (TEM). Result from microscopic observation showed that the M. malabathricum extract damaged the cell�s shape by rupturing the surface and the wall, causing the cytoplasm to leak. The assay using propidium iodide (PI) as the fluorescence dye showed that it was absorbed into the observed cell through flow cytometry analysis. The absorption of propidium iodide in treated cell confirmed the possibility of disturbance in the permeability of the cell membrane�s structure. From the microscopic observation and cytometry analysis, it can be concluded that acetone extract of M. malabathricum act as anti-bacteria agent that cause damage to the cell wall and disturb the permeability of the membrane structure. � 2014, Malaysian Society of Applied Biology. All rights reserved.