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This study was to evaluate the potential antibacterial activity of the methanolic
extracts of selected Sri Lankan traditional rice varieties (STRV) against bacteria
causing skin infections. Five STRV including Kalu Heenati, Pokkali, Rathdal, Kahawanu
and Sudu Murunga were used for in vitro antibacterial assays. Concentrations of
rice extracts used for the assays were 1000 pg/mL and 2000 pg/mL from the each
extract. The antibacterial activity was evaluated against common bacteria causing
skin and soft tissue infections [Staphylococcus aureus (ATCC 25923), Pseudomonas
aeruginosa (ATCC 27853), Escherichia coll (ATCC 25922)] and three clinical isolates
of Methicillin resistant staphylococcus aureus (MRSA)) by the well diffusion method
and viable colony count technique. All the selected Sri Lankan traditional rice extracts
exhibited a potent antibacterial activity against Staphylococcus aureus with minimum
bactericidal concentrations (MBC) of 200 pg/mL [minimum incubation time(MIT); 30
min] for Rathdal, 200 pg/mL (MIT; 60 min) for Kalu Heenati, Pokkali and Kahawanu,
and 2000 pg/mL (MIT; 60 min) for Sudu Murunga. Extracts of Kalu Heenati and Rathdal
showed the largest inhibition zones. Kalu Heenati, Pokkali and Rathdal showed an
efficacious inhibitory activity against MRSA (MBC; 200 pg/mL, MIT; 60 min), whereas
the highest inhibitory activity was observed for Rathdal. Only the extract of Kalu
Heenati demonstrated a slight activity against Pseudomonas aeruginosa. None of
the rice extracts studied evinced an antibacterial activity against Escherichia coli. The
present study highlights the importance of STRV as a potential source of antibacterial
compounds associated with skin infections. Selected STRV show potent antibacterial
activity mainly against Gram positive bacteria. Methanolic extract of Rathdal and Kalu
Heenati showed a high efficacious inhibitory effect against Staphylococcus aureus
and MRSA. The results of this study facilitate the use of STRV in traditional medicinal
practices to cure bacteria-borne skin diseases.
