Background: Many people suffer from acute pharyngitis which is caused by bacteria, especially Streptococcus pyogenes. Patients consume antibiotics even though antibiotic drugs have been causing adverse effects. Ten Thai medicinal plant species commonly used for treating acute pharyngitis may reduce the use of antibiotics.
Objective: To determine the antimicrobial activity of ten Thai medicinal plant species most commonly used for acute pharyngitis.
Material and Method: Plant materials were extracted with 95% ethanol or distilled water then concentrated and dried.
Antimicrobial activity of ten Thai medicinal plant species were determined using two standard assays, broth dilution method for minimal inhibitory concentration value (MIC) and agar dilution method for minimal bactericidal concentration value (MBC), against microorganisms that cause acute pharyngitis.
Results: The ethanolic extract of Garcinia mangostana showed the strongest activity of both assays, MIC value in range of 0.6-9.8 μg/ml and MBC value in range of 1.2-625 μg/ml, which inhibited all the bacteria tested and particularly inhibited S. pyogenes ATCC 19615 as the most common cause of acute pharyngitis with the value of MIC and MBC at 0.6 and 1.2 μg/ml, respectively. The second highest antimicrobial activity was the ethanolic extract of Glycyrrhiza glabra with MIC value in range of 39-156 μg/ml and MBC value in range of 78-312 μg/ml and it showed strong activity against S. pyogenes ATCC 19615, S. pneumoniae ATCC 49619 and S. mutans ATCC 25175 with the value of MIC and MBC at 39 and 78 μg/ml, respectively.
Conclusion: The ethanolic extract of G. mangostana and G. glabra are the two best choice for acute pharyngitis treatment.

Keywords: Acute pharyngitis, Thai traditional medicine, Antimicrobial activity, Garcinia mangostana, Glycyrrhiza glabra