Antibacterial and cell envelope damaging properties of different solvent extracts of Rhus chinensis Mill against E. coli and Staphylococcus aureus

Abstract

<em>Rhus chinensis</em> mill., is a member of the Anacardiaceae family and it is known for treating diarrhoea, dysentery, food poisoning and gastritis. <em>R. chinensis</em> contains a wide array of substances that can cure various infectious diseases. These substances are biologically active components also known as secondary metabolites or phytochemicals, which help to combat numerous diseases in the modern era. The decoction of the fruits of <em>R. chinensis</em> is useful for the treatment of dysentery, diarrhoea, indigestion and exhibit potential anticancer, antiviral, antimicrobial, antidiarrhoeal and anti-inflammatory activities.<br><br> Extracts of aqueous, ethyl acetate and methanol were tested against microorganisms and demonstrated antibacterial activity. The sample preparation for the SEM study was done according to the method described by Borthakur and Joshi. At the minimum inhibitory concentration (MIC) and concentration of 400 mg/mL the test bacteria <em>E. coli </em>and <em>Staphylococcus aureus </em>were treated with methanol extract and kept at 37ºC overnight for incubation. After incubation, the bacterial cultures were centrifuged for 20 min at 4^oC at 1000 rpm, then washed three times with 0.1M sodium cacodylate buffer (pH 7.3) and three times with distilled water by centrifuging for 3 min at 3000 rpm. <em>R. chinensis</em> exhibited significant antibacterial activity. The result of time kill assay of <em>E. coli</em> treated with methanol extract exhibited a twofold log reduction in the bacterial count at 90 min for MIC (12.5 mg/mL) and 60 min for 2 x MIC (25 mg/mL). The bacterial cells treated with the methanolic extract of <em>R. chinensis</em> revealed the leakage of cellular materials which exhibited absorbance at the wavelengths of 260 nm and 280 nm.