In the present study, 19 medicinal plant extracts were examined for antimicrobial activity against Propionibacterium acnes
and Staphylococcus epidermidis. The results showed that 13 extracts could effectively inhibit the growth of
Propionibacterium acnes. Among those, the extracts of Senna alata, Eupatorium odoratum, Garcinia mangostana, and
Barleria lupulina showed strong inhibitory effects (zone of inhibition ≥15 mm). Interestingly, Hibiscus sabdariffa, Garcinia
mangostana, Eupatorium odoratum, and Senna alata extracts showed promising antibacterial activities against both
Propionibacterium acnes and Staphylococcus epidermidis. The remaining 15 plant extracts had no detectable activity
against Staphylococcus epidermidis. Subsequent experiments were conducted to determine inhibitory concentrations of all
selected plant extracts. Garcinia mangostana showed the greatest antimicrobial effect. The MIC values against both
organisms were equal (0.039 mg/ml) and the MBC values were 0.039 and 0.156 mg/ml against Propionibacterium acnes
and Staphylococcus epidermidis, respectively (Table 1). The same amount of MIC and MBC obtained from this plant
against Propionibacterium acnessuggested that Garcinia mangostana extract could possibly act as a bactericidal agent to
this microorganism. In addition, the Houttuynia cordata extract also showed good antimicrobial effects against
Propionibacterium acnes with a MIC of 0.039 mg/ml but a high concentration was required to kill both Propionibacterium
acnes and Staphylococcus epidermidis as compared to the Garcinia mangostana extract. Two plant extracts, Senna alata
and Eupatorium odoratum, showed outstanding antimicrobial properties against Propionibacterium acnes based on the disc
diffusion assay, each had a MIC value of 0.625 mg/ml and a MBC of 1.25 mg/ml for Propionibacterium acnes