Inhibitory Effects of Green Tea Leaf Stalk Extracts on Colibactin-producing Escherichia coli and Colorectal Cancer Cells

¹ Department of Biology, Faculty of Science, Chiang Mai University, Chiang Mai 50200, Thailand
² Master of Science Program in Applied Microbiology (International Program), Faculty of Science, Chiang Mai University, Chiang Mai 50200, Thailand
³ Natural Extracts and Innovative Product for Alternative Healthcare Research Group, Faculty of Science, Chiang Mai University, Chiang Mai 50200, Thailand

^* Corresponding author: This email address is being protected from spambots. You need JavaScript enabled to view it.

Abstract

Colorectal cancer (CRC) is the third most commonly diagnosed cancer and the second leading cause of cancer-related deaths worldwide. Colibactin-producing Escherichia coli strains, particularly those carrying the pks gene cluster, have been increasingly detected in CRC patients, complicating treatment and highlighting the need for alternative therapeutic strategies. Tea (Camellia sinensis var. assamica) leaf stalks, a byproduct of tea processing, are often discarded during production, even though they are rich in bioactive compounds and have been less studied for their biological activities. This study evaluated young and mature green tea leaf stalk extracts for their chemical compositions, antioxidant activity, antibacterial activity, and cytotoxicity against HT-29 and Caco-2 colorectal cancer cells. The result revealed that tea leaf stalk extracts contained the phenolics and flavonoids compounds that related to antioxidant activity. In addition, young and mature green tea leaf stalks contained the bioactive compounds including epigallocatechin gallate (EGCG) and catechin by HPLC detection. For antibacterial activity, the young and mature green tea leaf stalk extracts exhibited the lowest MIC and MBC values at 62.5-250 mg/ml against all isolates of colibactin-producing E. coli (BAI, BA2, CA5, HA2, and VA2). Furthermore, cytotoxicity assay was showed that mature tea leaf stalk extract effectively inhibited HT-29 and Caco-2 cells, with lower IC50 values of 0.402 ± 0.029 mg/ml and 0.195 ± 0.028 mg/ml, respectively comparing to young tea leaf stalks (0.627 ± 0.044 mg/ml and 0.218 ±0.035 mg/ml). These new findings suggested that young and mature green tea leaf stalks are a promising natural source of bioactive compounds with potential antioxidant, antibacterial and anticancer effects, providing a safer alternative or complementary approach to conventional CRC therapy while mitigating associated side effects.