In vitro antibacterial activity of Sri Lankan orthodox black tea (Camellia sinensis L.) belonging to different agro-climatic elevations

Abstract

Objective: To investigate the antibacterial properties of three grades of orthodox Sri Lankan black tea belonging to the three agro-climatic elevations. Methods: Methanloic extracts of orange pekoe (OP), broken orange pekoe fannings (BOPF) and Dust No. 1 belonging to three agro-climatic elevations (low, mid and high grown) were made and tested in vitro (concentration: 300 µg/disc) against Gram-positive pathogenic bacteria, Staphylococcus aureus (ATCC 25923) (S. aureus) and Bacillus cereus (ATCC 11778) (B. cereus), and two Gram-negative bacteria Pseudomonas aeruginosa (ATCC 9027) (P. aeruginosa) and Escherichia coli (ATCC 35218) (E. coli), using agar disc diffusion assay. Gentamycin (10 µg/disc) was used as the positive control and methanol as the negative control. Minimum inhibitory concentration (MIC) values were evaluated, using micro dilution method. Results: None of the tea extracts exerted an antibacterial action against P. aeruginosa and E. coli. In contrast mild to moderate antibacterial activity was exerted against S. aureus and B. cereus. Further gentamycin exhibited strong antibacterial activity against all the four bacterial species. Further low MIC values were evident for tea samples against the two Gram-positive bacteria. The order of anti-bacterial activity for tea extracts was Dust No. 1 > BOPF > OP. Conclusions: It is concluded that Sri Lankan orthodox black tea belonging to Dust No. 1, BOPF, and OP pocess in vitro antibacterial activity against S. aureus and B. cereus but not against Gram-positive bacteria P. aeruginosa and E. coli. Article history: