Antibacterial Activity of Rhodomyrtus tomentosa (Aiton) Hassk. Leaf Extract against Clinical Isolates of Streptococcus pyogenes

Ethanol extract of Rhodomyrtus tomentosa (Aiton) Hassk. leaf was evaluated for antibacterial activity against 47 clinical isolates of Streptococcus pyogenes. The extract exhibited good anti-S. pyogenes activity against all the tested isolates with similar minimum inhibitory concentration (MIC, 3.91-62.5 mu g mL(-1)) and minimum bactericidal concentration (MBC, 3.91-62.5 mu g mL(-1)) ranges. No surviving cells were detected at 16 h after treatment with 8 x MIC of the extract. The extract-treated cells demonstrated no lysis and cytoplasmic leakage through the bacterial membrane. Electron micrographs further revealed that the extract did not cause any dramatic changes on the treated cells. Rhodomyrtone, an isolated compound, exhibited good anti-S. pyogenes activity (14 isolates), expressed very low MIC (0.39-1.56 mu g mL(-1)) and MBC (0.39-1.56 mu g mL(-1)) values. Rhodomyrtus tomentosa leaf extract and rhodomyrtone displayed promising antibacterial activity against clinical isolates of S. pyogenes.