As scientific research continues to advance, the antibacterial and antiviral effects of tea are gradually being revealed. These effects have already been successfully applied in drug development, food preservation, and daily chemical products.
I. Antibacterial Effects of Tea
1. Antibacterial Effects and Oral Health
Streptococcus mutans is the primary pathogenic bacterium responsible for human dental caries. Studies show that tea polyphenols have a strong inhibitory effect on Streptococcus mutans (more potent than grape polyphenols), with potential for development into antibacterial drugs for treating or preventing dental caries. They can be added to oral care products to enhance caries prevention. For example, research from Pace University in the U.S. indicates that Toothpaste containing white tea extract has enhanced antibacterial effects. Additionally, Black Tea generally exhibits better inhibitory effects against Streptococcus mutans compared to green tea. Studies have shown that the minimum inhibitory concentrations (MICs) of green and black tea against Streptococcus mutans are 150 mg/mL and 50 mg/mL, respectively, within a concentration range of 100–400 mg/mL, indicating that black tea is more effective at the same concentration.
Porphyromonas gingivalis and Prevotella spp. are two important periodontal pathogens. Green tea extracts exhibit good inhibitory effects against these bacteria. Studies have shown that after treatment with green tea extracts, the number of periodontal pathogens in the mouth significantly decreases. Furthermore, studies have indicated that the minimum bactericidal concentration (MBC) and MIC values of tea polyphenols against nine suspected periodontal pathogens are lower compared to five other Chinese herbal extracts (magnolol, baicalin, emodin, gallnut extract, and berberine), suggesting that tea polyphenols have stronger inhibitory capabilities.
2. Antibacterial Effects and Gastrointestinal Health
Research finds that tea polyphenols not only inhibit harmful intestinal bacteria but also promote the growth of beneficial intestinal bacteria. Feeding calves diets containing green tea extract results in a significant increase in the content of beneficial bacteria such as lactobacilli and bifidobacteria in their intestines, while the number of harmful bacteria like Clostridium perfringens significantly decreases, reducing Diarrhea and mortality rates.
Escherichia coli O157:H7 is a pathogen that can cause human gastrointestinal diseases. Studies show that when the concentration of Caffeine is above 0.5%, it has a very noticeable inhibitory effect on E. coli O157:H7. The inhibitory effect is significantly enhanced when green tea extract is combined with sodium chloride (NaCl). Enterotoxigenic Escherichia coli is an important pathogen that causes diarrhea in humans and young livestock. Research has found that green and black tea extracts can significantly inhibit enterotoxigenic E. coli's interference with intestinal fluid and electrolyte balance. Aeromonas hydrophila is another typical pathogen affecting humans, livestock, and fish, which can cause diarrhea, food poisoning, and secondary infections in humans. Studies have found that adding green tea extract to tilapia feed can improve the fish's resistance to Aeromonas hydrophila.
Helicobacter pylori is closely related to chronic gastritis, peptic ulcers, low-grade malignant gastric mucosa-associated lymphoid tissue lymphoma, and gastric cancer. Tea has therapeutic or preventive effects against various gastric diseases caused by Helicobacter pylori. Studies show that green tea, which is rich in polyphenols, has an inhibitory effect on Helicobacter pylori and can be used to treat or prevent various gastric diseases including gastric cancer and ulcers. The minimum inhibitory concentrations (MICs) of epigallocatechin gallate (EGCG) and epicatechin (EC) against Helicobacter pylori are 50–100 μg/mL and 800–1,600 μg/mL, respectively, suggesting that the concentration of tea polyphenols in daily tea consumption may have a noticeable inhibitory effect on Helicobacter pylori. Additionally, different types of tea exhibit varying degrees of inhibitory effects against Helicobacter pylori. A study comparing the inhibitory effects of extracts from four major types of tea (green, black, Oolong, and white) and extraction times on Helicobacter pylori found that all teas showed inhibitory effects when the extraction time was 5 minutes. However, only Darjeeling black tea and Teshu white tea exhibited inhibitory effects against Helicobacter pylori when the extraction time was 2 minutes.
3. Antibacterial Effects and Skin Health
Green tea extracts have a strong inhibitory effect on human skin pathogens. A study analyzed and compared the effects of EGCG and other antifungal components on clinically isolated dermatophytes and found that all tested strains were more sensitive to EGCG than fluconazole and flucytosine. The antifungal effects of EGCG were about four times higher than those of fluconazole and four to sixteen times higher than those of flucytosine. Additionally, green tea extracts also have inhibitory effects against Staphylococcus epidermidis, Micrococcus luteus, and Brevibacillus brevis. Saponins in tea leaves are also components with antifungal activity, showing good inhibitory activity against dermatophytic fungi such as Microsporum audouinii.
4. Antibacterial Effects and Food Preservation
The antibacterial components in tea can be used as natural preservatives for food preservation. For example, applying green tea extracts to frozen white shrimp can significantly inhibit microbial growth. Using green tea extracts for oyster meat preservation can extend the shelf life of the meat. Theaflavins are natural antibacterial agents that can improve the safety and hygiene of food as food additives. Studies show that the minimum inhibitory concentrations (MICs) of tea polyphenols and several main catechins against beneficial bacteria in food (such as lactobacilli and bifidobacteria) are 2–5 times higher than those against harmful bacteria.
Tea polyphenols have good inhibitory effects against Bacillus stearothermophilus, helping to prevent food spoilage. Green tea extracts can inhibit the germination and growth of spores of Clostridium perfringens during the cooling process of cooked beef, chicken, and pork. Additionally, dark tea also has certain inhibitory capabilities against bacilli. Studies have found that extracts from Fu brick tea have inhibitory effects against some food pathogens, particularly spore-forming bacteria such as Bacillus cereus, Bacillus subtilis, Clostridium perfringens, and Clostridium sporogenes.
5. Antibacterial Effects and Clinical Medicine
Staphylococcus aureus (SA) is a primary pathogen causing bacterial food poisoning and hospital-acquired infections. Studies have found that green tea extracts have a good inhibitory effect on Staphylococcus aureus, with the minimum inhibitory concentration (MIC) of EGCG being 58 mg/L. Moreover, using green tea extracts in combination with sodium chloride (NaCl) enhances the antibacterial effect of the extracts against Staphylococcus aureus.
Methicillin-resistant Staphylococcus aureus (MRSA) is resistant to multiple antibiotics. Studies have found that ascorbic acid (Vc) can increase the stability of EGCG, thereby enhancing its inhibitory effect on MRSA. The MIC of EGCG alone against MRSA is 64 μg/mL, while the MIC is reduced to 32 μg/mL when ascorbic acid is added. Different types of tea have certain antibacterial effects against MRSA, with stronger effects observed in white tea, green tea, and oolong tea.
Pseudomonas aeruginosa is a bacterium with low pathogenicity but strong antibiotic resistance, widely present in nature and commonly involved in wound infections. Studies have found that surfactants and preservatives can enhance the inhibitory effect of green tea extracts against Pseudomonas aeruginosa when the pH is 5.0, 6.5, and 8.0. Tea polyphenols can inhibit Pseudomonas aeruginosa by disrupting the cell membrane, with significant inhibitory effects at concentrations above 0.75 mg/mL.
Stenotrophomonas maltophilia and Acinetobacter baumannii are important pathogens in hospital infections and are resistant to most antimicrobial drugs. Studies have shown that theaflavins have a clear inhibitory effect against these pathogens. Combining theaflavins with EC significantly enhances the inhibitory effect. Additionally, studies have indicated that EGCG is a highly effective antibacterial agent against antibiotic-resistant Acinetobacter baumannii.
Mycobacterium tuberculosis