Anti-Streptococcus pyogenes Activity of Selected Medicinal Plant Extracts Used in Thai Traditional Medicine

Purpose: To evaluate the anti-Streptococcus pyogenes activity of selected medicinal plants used in Thai traditional medicine.Methods: Sixty-nine extracts of 51 selected Thai medicinal plant species were tested for anti-S. pyogenes activity by paper disc agar diffusion and broth microdilution methods.Results: Ten plants including Boesenbergia pandurata (Roxb.) Schltr., Cinnamomum bejolghota (Buch.-Ham.) Sweet, Cinnamomum porrectum (Roxb) Kosterm, Eleutherine americana Merr., Gymnopetalum cochinchinensis (Lour.) Kurz, Piper betle L., Quercus infectoria G. Olivier, Quisqualis indica L, Rhodomyrtus tomentosa (Aiton) Hassk., and Walsura robusta Roxb. demonstrated good antibacterial activity against S. pyogenes NPRC 101. These plants were selected and further evaluated for their anti-S. pyogenes activity against 11 isolates of S. pyogenes from patients with upper respiratory tract infections. Three plants including Boesenbergia pandurata, Eleutherine americana, and Rhodomyrtus tomentosa exhibited good antibacterial activity against all S. pyogenes isolates and produced similar activities against different tested isolates. Boesenbergia pandurata and Rhodomyrtus tomentosa demonstrated antibacterial activity with the same minimal inhibitory concentration (MIC) and minimal bactericidal concentration (MBC) range of 3.91 - 31.25 μg/ml whereas Eleutherine americana displayed MIC and MBC values of 250 and 250-500 μg/ml against all S. pyogenes isolates.Conclusion: Boesenbergia pandurata, Eleutherine americana, and Rhodomyrtus tomentosa have great antibacterial potentials against S. pyogenes.Keywords: Antibacterial activity, Boesenbergia pandurata, Eleutherine americana, Rhodomyrtus tomentosa, Streptococcus pyogenes, Thai medicinal plant, Upper respiratory tract infection