Antibacterial Activity of Tea

Tea, a popular beverage enjoyed by many around the world, has been shown to possess various health benefits. In recent years, research has revealed that tea also possesses antibacterial properties, with some studies indicating its potential to inhibit the growth of certain bacterial strains. This article aims to explore the antibacterial activity of tea and its components, providing an overview of the research conducted in this field.

Bacteriostatic and Bactericidal Activity of Tea

Tea has been found to have antibacterial properties, with several studies reporting that adding tea powder to nutrient agar can inhibit the growth of pathogenic bacteria such as Staphylococcus aureus, Salmonella, Vibrio cholerae, and Shigella dysenteriae. Additionally, extracts of black tea, Japanese green tea, and coffee have been found to be bactericidal against certain strains of bacteria, with black tea and Japanese green tea showing stronger activity against Staphylococcus aureus and Vibrio cholerae than Chinese tea and coffee. Tea infusion has also been found to be effective against some types of fungi, including Trichophyton mentagrophytes and T.rubrum, but not Candida albicans.

Antibacterial Activity of Tea Components

Tea has compounds called polyphenols that are responsible for its antibacterial properties. Catechins are a type of polyphenol found in tea and they make up 5-10% of its dry weight. Catechins can inhibit the growth of many types of bacteria, including Staphylococcus aureus, Salmonella typhosa, and Vibrio parahaemolyticus. The larger molecules in black tea, called theaflavins and thearubigins, also have antibacterial properties.

Green tea contains over 100 volatile compounds and black tea contains over 300. Some of these compounds, such as δ-cadinene, caryophyllene, and nerolidol, have antibacterial and antifungal properties. However, the concentration of these compounds in a cup of tea is not strong enough to effectively control harmful microorganisms.

Anti-Vibrio Cholerae 01 Activity of Tea

Tea has antibacterial and bactericidal effects against various bacteria that cause diarrheal diseases, including Vibrio cholerae. Tea extract can kill Vibrio cholerae within 1 hour and can also inhibit the toxic activity of purified cholera toxin. The gallate moiety of the molecule is important for the growth inhibitory activity of catechins. EGCG, ECG, and ECG at a concentration of 33 µg/ml could inhibit the hemolysis of Vibrio cholerae by 100%, 65%, and 69%, respectively. Theaflavin digallate inhibited the hemolysis of cholera hemolysin by 75% and inhibited the hemolysis of a-toxin by 92% at a concentration of 2 µM. The tertiary structure of the catechin or theaflavin and the active site of hemolysin play an important role in the anti-hemolysin activity. The black tea extract and tea catechins have been tested in animals for their anti-cholera toxin and anti-cholera infection effects.

Effect of Tea on Intestinal Microflora

Tea can affect the microorganisms in the intestines, which play a role in normal physiological functions and various diseases. The composition of the microflora can be influenced by factors such as age, diet, and stress. The normal microflora is primarily made up of lactic acid bacteria, but cancer patients have a higher amount of clostridia and eubacteria and fewer lactic acid bacteria. Elderly people have fewer bifidobacteria but more clostridia than younger people. A disturbance in the microflora can cause various diseases or abnormal physiological states. Green tea extract can inhibit the growth of clostridia, which are associated with a wide range of human diseases. Tea catechins, such as (-)-epicatechin gallate and (-)-epigallocatechin gallate, can also have strong inhibitory effects on C. difficile and C. perfringens. Tea polyphenols can affect the microflora of healthy volunteers, reducing the count and frequency of occurrence of C. perfringens and increasing the count of Bifidobacterium spp. and Peptococcaceae. Clostridia are thought to cause various diseases, such as sudden death, toxicity, mutagenesis, carcinogenesis, Alzheimer’s disease, and aging.

Anti-MRSA Activity of Tea

Toda et al. (1991) studied the effects of black tea and green tea extracts, as well as tea catechins, on MRSA and food poisoning strains of S.aureus. They found that tea infusion, (-)-epigallocatechin gallate (EGCG), and theaflavin digallate (TF3) inhibited the growth of all strains of MRSA and food poisoning S.aureus. Black tea at 2.5% and 5.0% showed a bactericidal activity against MRSA. EGCG at 250 µg/ml showed bactericidal activity against MRSA, but not against food poisoning S.aureus. Yamazaki (1996) found that the growth-inhibition of MRSA was clearly observed in distinct areas where subMIC concentrations of the tea extract and ß-lactam antibiotic had been applied. Lower levels of growth-inhibition or no inhibition were seen with oxacillin, carumonam, and non-ß-lactam antibiotics. Further examination of the combined effects of tea catechins and ß-lactam antibiotics against MRSA and the mechanisms involved is worthwhile.

Anti-Phytopathogenic Bacter ia Activity of Tea

Tea catechins, including crude catechins and their four components from green tea and the crude theaflavins from black tea, have inhibitory effects on phytopathogenic bacteria that tend to infect commonly cultivated vegetables. Tea polyphenols could be safe potential agricultural chemicals against vegetable diseases. Pyrogallol catechins (EGC and EGCG) were more effective than catechol catechins (EC and ECG), and ECG and EGCG, which have a galloyl radical, showed significant activity against certain plant pathogenic bacteria. Among these catechins, EGCG demonstrated the highest inhibitory activities against all plant pathogenic bacteria tested. Tea catechins are useful and safe for the prevention of bacterial diseases of plants.

The Bactericidal Mechanism of Tea Catechins

Tea catechins have bactericidal and anti-toxin activities that indicate that they deactivate proteins. They affect mammalian cells by inducing lymphocyte proliferation, immunoglobulin synthesis, mitogenicity of B-lymphocytes, and stimulating interleukin production of human leukocytes at low concentrations. Gram-positive bacteria are more sensitive to the growth inhibition and bactericidal activities of tea catechins than Gram-negative bacteria. The strongest inhibitor and bactericidal agent is (-)-epigallocatechin gallate (EGCG). The weakest inhibitor is (-)-epicatechin (EC), which is non-bactericidal. EGCG causes rapid leakage of 5,6-Carboxyfluorescein (CF) entrapped in the intraliposomal space made of egg-yolk phosphatidylcholine (PC), and the extent of CF-release reaches 50% within 5 min and slowly increases thereafter in a concentration-dependent manner. The membrane damage caused by EGCG enhances the penetration of catechin itself into the interior of the cell. The surface charge of the target membrane is important in catechin susceptibility. The low catechin susceptibility of Gram-negative bacteria may be due partially to the presence of a strong negative charge of lipopolysaccharide at the exterior of the outer membrane. Catechins interact with the membrane and damage the lipid bilayers possibly by directly penetrating the lipid bilayer and disrupting the barrier function. However, it is still unknown how bactericidal catechins damage the bacterial cell membrane.