Antibacterial Activity Of The Crude Extract Of Chinese Green Tea (Camellia Sinensis) On Listeria Monocytogenes

摘要

The antibacterial activity of the methanol and aqueous extract of Camellia sinensis on Listeria monocytogenes were investigated using Agar-gel diffusion, paper disk diffusion and microbroth dilution techniques. The results obtained showed that methanol and water extract exhibited antibacterial activities against Listeria monocytogenes. The leave extract produced inhibition zone ranging from 10 .0 – 20.1mm against the test bacteria. The methanol extracts of the test plant produces larger zones of inhibition against the bacteria than the water extract. The minimum inhibitory concentration (MIC) for the methanol and water leave extract was 0.26mg/ml and 0.68mg/ml respectively. Introduction Green tea is a non-fermented tea. The tea is an infusion of flavorful leaves that has been consumed for centuries as a beverage and is valued for its medicinal properties. The phytochemical screening of tea revealed the presence of alkaloids, saponins, tannins, catechin and polyphenols [1,2]. Toda et al [3] also showed that moderate daily consumption of green tea killed Staphylococcus aureus and other harmful bacteria. Recent reports however indicate the tea's antibacterial and bactericidal properties on various bacterial strains isolated from patients with infected root canal [4]. Subsequently, several studies on the antimicrobial properties of Japanese tea have been reported [3,5,6]. The antibacterial activity of Turkish tea against Campylobacter sp and the protective activity of tea against infection by Vibrio cholera 01 have also been reported [7,8]. Listeria monocytogenes a gram-positive bacterium, that is salt resistant and highly adapted. This organism is motile, psychrophil, and occurs everywhere in the environment. It is isolated from silo, vegetable, dairy foods, red meat, ready-to-eat food products etc. it causes listeriosis in human and other animal and birds. The organism is recognized as a food-borne pathogen. Prompted by these report, the study is therefore aimed at investigating the antibacterial activity of Chinese green tea on Listeria monocytogenes. Materials and Methods Plant Collection The air-dried leaves of Chinese green tea (Camellia sinensis) were collected from Zhejianq provincial Department of Agriculture, Hangzhou, China. The leaves were cut into pieces and grinded into powdery form using a sterile electric grinder. The soluble ingredients in the grounded plant part was then extracted by solubilization using ethanol and water as different solvents. Aqueous Extraction The aqueous extractions of the water-soluble ingredients were carried out using the method as described by Asuzu [9]. 15g of each of the grounded leaves were extracted by successive soaking for 2 days using 35ml of distilled water in a 250ml sterile conical flask. The extracts were filtered using Whatman filter paper No 1. The filtrates were concentrated in vacuum at 60°C and stored in universal bottles and refrigerated at 4°C prior to use. Methanol Extraction The methanol extractions of the active ingredient of the leaves were carried out using the method as described by Harbone [10]. 25g of the grinded leaves were soxhlet extracted using 250ml of 95% methanol. The extraction lasted for six hours. The volatile oil obtained was concentrated by evaporation using water bath at 100°C.Test OrganismThe strain used in this work was Listeria monocytogenes type 4a (food origin) obtained from culture collection centre at Hebrew University Israel. The bacteria was maintained by weekly transfer in a chemically defined medium and tryptic soy broth (TSB) and distributed in 5ml volumes in screw-capped tubes. Cells were grown at 37°C for 48h and cultures were kept at 4°C. Antibacterial susceptibility testingThe antibacterial tests of the leave extracts were tested on the test bacteria using the agar-gel diffusion inhibition test and paper disk diffusion inhibition test. In the agar-gel diffusion inhibition test as described by Opara and Anasa [11], 0.2ml of a 24h broth