In-vitro antimicrobial and synergistic properties of water soluble green and black tea extracts

Green and black teas extracts are known for their antibacterial activity against many pathogenic microorganisms. These studies have been necessitated by the need to combat the recent rise of drug-resistant human pathogens which is becoming a common occurrence in the world making easily manageable infections to become life threatening illnesses. This study evaluated the antimicrobial activity of water soluble green and black tea extracts from a high quality Kenyan tea clone TRFK 6/8 against antibiotic resistant Escherichia coli ATCC 25922 and Staphylococcus aureusATCC 25923 using agar well diffusion method. Green and black tea extracts effectively inhibited the growth of both E. coli ATCC 25922 and S. aureus ATCC 25923 at concentrations of 0.1 and 0.05 mg/ml, respectively after 24 h. Green tea extracts and gentamicin showed greater zone of inhibition compared to penicillin G. In addition, the possible synergistic activity of water soluble green tea extract and antibiotics was also determined using agar well diffusion method. A combination of penicillin G and green tea extract inhibited the growth of E. coli ATCC 25922 and S. aureus ATCC 25923 compared to penicillin G alone while gentamicin exhibited an additive and antagonistic effect depending on tested bacteria. Green and black tea extracts can be used as an antimicrobial agent and also green tea extract can be used in combination with penicillin G to manage resistant pathogenic bacteria. Furthermore, tea which is a proven safe, cheap and readily available compound can be used in more ambitious trials to test the antimicrobial efficacy and chemo-preventive effects in animal and human models.   Key words: Green tea, black tea, antimicrobial activity, synergistic activity, gentamicin, penicillin G.