Effects of Kenyan black tea water soluble components on theaflavins interaction with antibiotics against selected pathogenic bacteria

Abstract

Water soluble components derived from black tea contain active antibacterial compounds, that can be utilized in combined antibiotic-herb therapy to combat bacterial resistance. This strategy is more advantageuos than using single therapy as it is more effective and has minimal side effects. However, it is not clear if the major bioactive compounds interacts with other water soluble compounds, which inturn affects their interaction with antibiotics. This research therefore aimed at comparing the antibacterial activities of hot water extract of black tea having 18μg/ml of theaflavins and 18μg/ml of isolated theaflavins and their combination with antibiotics such as ampicillin. Their combined effects with antibiotics were determined using disk diffusion and modified Checkerboard method. The chi-square test was used to test the null hypothesis, which stated that water soluble components have no effect on theaflavins interaction with antibiotics. The water soluble components of black tea extract were extracted with hot water and theaflavins in it was measured using Flavognost method. Similar amount of theaflavins were extracted using organic solvents and silica gel column chromatography. The concentrates of hot water extract and isolated theaflavins showed synergistic activity with selected antibiotics. However the level of synergism differed significantly at P<0.05, with isolated theaflavins having higher level. The difference in inhibitory effect between combined concentrates of hot water extract and isolated theaflavins with MIC (10.4 μg/ml) of ampicillin against S. typhi was significant at (χ2=0.56; P<0.05). The differences in inhibitory effect was also significant at (χ2=0.699; P<0.05) between the two black tea extracts combinations with MIC (4.3 μg/ml) of norfloxacin against P. aeruginosa. The combination of concentrates of hot water extract and isolated theaflavins with MIC (2 μg/ml) of ciprofloxacin differed significantly in level of inhibition at (χ2=1.98; P<0.05) against S. aureus. When the concentrates of the two black tea extracts were combined with MIC (5.25 μg/ml) of tetracycline, the inhibitory effect differed significantly at (χ2=2.27; P<0.05) against E. aeruginosa. It was also significant at (χ2=0.4; P<0.05) when concentrates of the two black tea extracts were combined with MIC (12 μg/ml) of chloramphenicol against E. coli. The differences in inhibitory effect observed were attributed to interactions within the tea infusion between water soluble components and theaflavins. Theaflavins in black tea infusion are being partially antagonized by one or more chemical components in it lowering the overall activity. However, the pattern of activity of isolated theaflavins and hot water extract of black tea were similar. This suggests that the theaflavins are the principal bioactive compounds in black tea infusion despite the existence of interaction. Isolated theaflavins and hot water extracts of black tea restored the activity of lower concentrations of antibiotics below MIC to susceptible breakpoints. The two black tea extracts together with antibiotics can be used in treatment and prevention of bacterial infections.