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J Altern Complement Med. 2007 Dec;13(10):1119-24. doi: 10.1089/acm.2007.7033.

Selective microbiologic effects of tea extract on certain antibiotics against Escherichia coli in vitro.

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Laboratory of Nutrition Research, National Nutrition and Food Technology Research Institute, Shaheed Beheshti Medical University, Tehran, Iran.



This study evaluated the microbiologic effects of black tea, compared to green tea, alone and in conjunction with selected antibiotics against Escherichia coli, the common cause of intestinal and urinary tract infections.


This study was an in vitro evaluation of antibacterial effects of tea extracts.


Black and green tea extracts were analyzed by using high-performance liquid chromatography to compare their major polyphenol profiles. Different concentrations of the extracts or gallic acid (GA), the phenolic compound found with high concentration in the black tea extract, were employed for bacterial sensitivity tests, using pour plate and disc diffusion methods. The latter was used to evaluate the interactions between the extracts and certain anti-E. coli antibiotics.


GA in black tea extract and epigallocatechin and epigallocatechin gallate in green tea extract are present in the highest concentrations, respectively. At concentrations of 25 mg/mL, both black and green teas after 5 and 7 hours completely inhibited E. coli growth. GA at concentrations of 5, 10, and 25 microg/mL after 7, 5 and 3 hrs, respectively, inhibited bacterial growth. Both black and green tea extracts had either synergistic or antagonistic effects at different concentrations on selected antibiotics, while GA showed a synergistic effect with all the antibiotics tested in a dose-dependent manner. The effect was more prominent with amikacin and sulfamethoxazole.


The microbiologic effects of both black tea and green tea extracts on certain antibiotics against E. coli may vary, depending on the type of the tea extract (i.e., black vs. green), the amount of the extract, and the antibiotic being used.

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