Activity of tea polyphenols against vibrio species

Green tea is noted in the West and as well in the East because of its antimicrobial activity and antioxidant activity, and its overall beneficial effects on the health of humans. These benefits are related to the presence of polyphenols in green tea particularly flavonoids. Green tea catechins (GTC) constitute 60-90% of total flavonoids. GTC can be further divided into Epigallocatechin gallate (EGCG), Epigallocatechin (EGC), Epicatechin gallate (ECG) and Epicatechin (EC) and these have an important role in antimicrobial activity. During the present study all of these green tea catechins were found in the green tea extract (GTE) using liquid chromatography and mass spectrometry (LCIMS). In this study the activity of tea polyphenols against variety of gram negative and gram positive organisms was observed. In this study three vibrios (Vibrio parahaemolyticus along with Vibrio cholerae and Vibrio cholerae non -01) were found to be more sensitive to GTE than Staphylococcus aureus, Bacillus cereus and Listeria monocytogenes. Members of Enterobacteriacea showed no sensitivity to green tea extract using the hole in the plate assay. The MICs using GTE and the purified catechins (EGCG, ECG, EGC, EC) and also gallic acid (GA) against these three vibrios were also determined. The antibacterial activity shown was ascribed to the green tea catechins predominantly by epigallocatechin gallate (EGCG). Among the tested Vibrio parahaemolyticus was found to be most sensitive to the tested catechins. Various strains of parahaemolyticus (clinical and environmental) showed almost similar MICs against the EGCG. The antimicrobial activity of EGCG appears to be correlated with the possession of the trihydroxyphenyl, galloyl moiety. The effectiveness of catechins containing the galloyl moiety is related to their redox activity, and it was observed that under aerobic conditions of incubation larger zones of inhibition were produced compared to those produced under anaerobic conditions (P<0.05) at a level of 10% fresh green tea extract. This clearly suggests a role for oxygen in the antibacterial activities of tea catechins. Similarly, in the presence of purified catechins, larger zones of inhibition were observed under the aerobic incubation for all three vibrios (p<0.05). The zone of inhibition in this study was not significantly reduced in the presence of catalase as was found in the previous studies suggesting that factors other than the hydrogen peroxide production may be involved in the antibacterial activity. Antioxidant activity of green tea catechins (EGCG, EGC, ECG and EC) was measured using two different methods which are the ferric thiocyanate (FTC) method and peroxide value (PV) method. Both methods showed that EGCG was the best antioxidant. However the antioxidant activity shown by EGC, ECG and EC were different in both methods. In this study it was found that the effect of storage for 64 days at 4°C, reduced the activity of GTE and purified catechin EGCG by 13.3% for 10% GTE whereas a much clearer reduction (47%) was observed to lOmM EGCG. In concentrations exceeding their MICs, EGCG and ECG produced rapid death in populations of V. cholerae and V. parahaemolyticus in survival experiments. The data obtained from survival experiments with V. parahaemolyticus for various concentrations of EGCG (0.5, 1, 2 and 3mM) were fitted to a mathematical model which gave an estimated death rate. These results suggested that the damage caused to bacterial cell membranes could be a possible reason for the sharp decrease in the viable count. In this recent study the interaction of EGCG with V. parahaemolyticus was examined using a colorimetric method and this supported the possibility of adsorption of EGCG to cell membrane. Finally, the effect of EGCG on cell permeability was also assessed using bioluminescence assay and also growing cells at different temperatures. The results showed a massive release of A TP in presence of EGCG and so perhaps the killing effect could be due to ability of EGCG to bind with the cell membrane causing permeability surface changes resulting in the loss of cell viability with massive loss of ATP into the medium. However, growth temperature showed no significance (P>0.05) in inhibition.