Chemical compositions and antimicrobial activities of Athrixia phylicoides DC. (bush tea), Monsonia burkeana (special tea) and synergistic effects of both combined herbal teas

ABSTRACT

Objective: To determine the chemical compositions and evaluate the antimicrobial activity of bush tea (Athrixia phylicoides DC.), special tea (Monsonia burkeana) and synergy (combination of bush tea and special tea). Methods: Total polyphenols were determined using the methods reported by Singleton and Rossi (1965) and modified by Waterman and Mole (1994). Tannins were determined using vanillin HCL methods described by Prince et al. (1978). Total antioxidants were determined using the methods described by Awika et al. (2004). The micro dilution technique using 96-well micro-plates, as described by Eloff (1998) was used to obtain the minimum inhibition concentration (MIC) and minimum microbicidal concentration (MMC) values of the ethanol extracts against the microorganisms under study. The microbes strain used was Gram negative bacteria such as Escherichia coli, Klebsiella oxytoca, Proteus vulgaris, Serratia marcescens, Salmonella typhi, Klebsiella pneumonia; Gram positive bacteria such as Bacillus cereus, Staphylococcus aureus and a fungus Candida albicans. Results: The results demonstrated that special tea contains significantly higher content of total polyphenols (8.34 mg/100 g) and total antioxidant (0.83 mg/100 g) as compared to bush tea [total polyphenols (6.41 mg/100g) and total antioxidant (0.63 mg/100g)] and combination of bush tea and special tea [total polyphenols (6.42 mg/100 g) and total antioxidant (0.64 mg/100 g)]. There was no significant difference in tannins between bush tea, special tea and synergy. The results of antimicrobial activity (MIC and MMC) demonstrated that the ethanol extracts of bush tea, special tea and synergy possessed antimicrobial activity against all microorganisms at different zones. The MIC of bush tea ranged from 1.56 to 12.50 mg/mL while the MMC ranged from 0.78 to 12.50 mg/mL. Special tea's MIC ranged from 0.39 to 12.50 mg/mL while the MMC ranged from 0.01 to 12.50 mg/mL. The MIC of synergy ranged from 3.13 to 12.50 mg/mL while the MMC ranged from 3.13 to 12.50 mg/mL without positive synergistic effect recorded. Conclusions: Both bush and special tea contain total polyphenols, total antioxidants and tannins with special tea containing a significantly higher total polyphenols and total antioxidant as compared to bush tea and synergy. Bush tea, special tea and synergy possess antimicrobial activity at various degrees.