Abstract:
Ralstonia solanacearum, a soil-borne bacterium, is responsible for bacterial wilt in a
variety of solanaceous crops, leading to significant yield losses. Using antibacterial
agents to control bacterial wilt is expensive and may produce antimicrobial resistance.
Theaflavin, a polyphenolic compound obtained from tea (Camellia sinensis), has shown
antimicrobial effects previously. Hence, this study was carried out to evaluate the
activity of theaflavin against R. solanacearum. A 100mg/mL stock solution was
prepared using theaflavin powder and sterile distilled water as the solvent. A series of
dilutions was prepared using the above to obtain the concentrations: 50mg/mL,
25mg/mL, 12.5mg/mL, and 6.25mg/mL. Tetracycline was used as the positive control,
and sterile distilled water as the negative control. R. solanacearum was cultured on
Muller-Hinton agar overnight, and a fresh bacterial suspension (McFarland 0.2) was
prepared in Phosphate Buffer Solution. A well diffusion assay was performed on
Muller-Hinton agar for the aforementioned concentrations against R. solanacearum.
Antibacterial effect of theaflavin was measured by deducting the Diameter of the
Inhibition zone by sterile distilled water and from the diameter of the inhibition zone
due to theaflavin/ tetracyclin. All theaflavin concentrations tested inhibited R.
solanacearum. Along with the reducing concentration gradient, the size of the
inhibition zone decreased. The ZOIs were 11.50±0.7mm for 100mg/ml, 9.13±0.6mm
for 50mg/mL, 7.50 ±0.6mm for 25mg/mL, 5.38 ±0.3mm for 12.5mg/mL and
3.75±0.5mm for 6.25mg/mL. ZOI for tetracycline was 16.75±0.5. These findings
indicate that theaflavin has a concentration-dependent antibacterial effect against R.
solanacearum, suggesting that theaflavin may be an alternative to control bacterial
wilt.
