Methanolic Extract of Neem Leaf (Azadirachta indica) and its Antibacterial Activity Against Foodborne and Contaminated Bacteria on Sodium Dodecyl Sulfate-Polyacrylamide Gel Electrophoresis (SDS-PAGE)

To study the effect of neem extract on the growth and viable count of foodborne and contaminated bacteria and determine its active inhibitors. Different concentrations of methanolic extracts (200 mg/ml, 150 mg/ml, 100 mg/ml, 50 mg/ml and 25 mg/ml) were prepared. One-hundred microliters of standardized test organisms was treated with solvents or extract. The extract was tested against Gram-positive bacteria (Bacillus cereus, Bacillus subtilis, Listeria monocytogenes, Staphylococcus aureus, Clostridium perfringens and Micrococcus luteus) and Gram-negative bacteria (Salmonella typhimurium, Escherichia coli) using agar diffusion and minimum inhibitory concentration (MIC) analyses. Methanolic neem extract was highly effective at prohibiting the growth of Listeria monocytogenes and Staphylococcus aureus at a concentration of 50 mg/ml. However, methanolic neem extract, even at the highest tested concentration (200 mg/ml), did not prohibit Bacillus cereus and Bacillus subtilis growth. In addition, three bands of Staphylococcus aureus proteins of different molecular weights (more than 97 kDa, 50 kDa and at 18 kDa) disappeared during the neem extract and the four antibiotic treatments. Methanolic neem extract contains a photochemical substance, such as phenolic and flavonoids, that may inhibit the growth of foodborne bacteria.