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

Aqueous Extraction

Methanol Extraction

Test Organism

Antibacterial susceptibility testing

Minimum inhibitory concentration

Results

The methanol extract of the leave of Camellia sinensis showed various levels of antibacterial activity when tested by both methods. Whereas the aqueous extract showed antibacterial activity only when tested by the paper disc diffusion method (Table 1 –2). The methanolic extract of the leave of Camellia sinensis possess greater antibacterial properties against Listeria monocytogenes as against the water extract.

Table 2 showed the antibacterial susceptibility of the aqueous extract of the leave of Camellia sinensis on L. monocytogenes. There was no antibacterial or antilisteric activity of the aqueous leave extract on the test organism using Agar-gel diffusion. Higher diameter zones of inhibition was obtained with the paper disc method than with Agar-gel diffusion method on the test organism and for both extraction methods. The minimum inhibitory concentration (MIC) of the methanol extract 0.26mg/ml were lower than those of the extract of 0.68mg/ml as can be seen in table 3. This indicate that the extracts is very active and possess antilisteric properties.

Figure 1

Table 1: Antibacterial activity of the methanol extract of leave of Camellia sinensis on L. monocytogenes.

Figure 2

Table 2: Antibacterial activity of the Aqueous extract of leave of Camellia sinensis on L. monocytogenes

Figure 3

Table 3: Minimum inhibitory concentration of the leave extract of Camellia sinensis on L. monocytogenes.

Discussion

The result of the study showed that the leave extract of Camellia sinensis produced zones of inhibition against Listeria monocytogenes. This indicates the presence of potent antibacterial activity, which confirms its use as anti-infective.

Although both the methanol and water extract of the leave of Camellia sinensis produced inhibitory actions against. Listeria monocytogenes, methanol extracts showed more inhibitory effects than the water extract. This tends to show that the active ingredients in the leaves were better extracted with methanol than water. Akunyili et al [₁₃] observed a similar result when they worked with stem bark of Kigelia pinnata.

Toda et al [₁₄] reported that daily consumption of green tea can kill gram positive Staphylococcus aureus and other harmful bacteria. Also it have been reported [₁₅,₁₆,₁₇,₁₈,₁₉] that the green tea contain catechin and polyphenols. These compounds have been found to possess antibacterial and antiviral action as well as anticarcinogenic and antimutagenic properties. This suggests that these compounds could be responsible for the inhibitory of L.monocytogenes used in this study.

The two methods used to test the antibacterial activity of the leave extract proved to be good, but the paper disc diffusion method tend to show wider zones of inhibition than the agar-gel diffusion methods.

From the result obtained in Table 3, it showed that at low doses of 0.26mg/ml and 0.68mg/ml the crude extract of the methanol or probably the water extract would inhibit the effect of the aetiologic agent causing these diseases (listeriosis). This gives credence to its ethnopharmacological use as a remedy to treat infections and diseases caused by the organism.