The antibacterial activity of HNE was measured using disc diffusion assay followed by micro broth dilution assay in order to determine MIC. Although there were a wide range of solvent concentrations that exhibited the antibacterial activities (Table 1), the lowest concentration of each solvent was used to determine MIC (ethanol 60%, methanol 100% and acetone 20%). It was investigated that for ethanol 60% and methanol 100%, the concentration of the extracts must be equal or greater than 50 mg/ml to inhibit the growth of S.aureus, B.cereus and S. Typhimurium. However for acetone 20%, the concentration of 3.125 mg/ml could start inhibiting B. cereus but the concentration equal or greater than 50 mg/ml was required to inhibit S. aureus, , S. Typhimurium and E. coli.
The antimicrobial activities exhibited in HNE may result from their high TPC and antioxidant activities. The phenolic compounds from plant extracts can degrade the cell wall, disrupt the cytoplasmic membrane, cause leakage of cellular components, change fatty acid and phospholipid constituents, influence the synthesis of DNA and RNA and destroy protein translocation. A positive correlation between the phenolic content of the plant extract and the Gram positive and Gram negative pathogenic bacterial inhibition was observed and reported.