Screening of antibacterial activity of 20 Chinese herbal medicines in Yunnan

The 80% ethanol extracts from 20 Chinese herbal medicines collected in Yunnan Province, China, were screened for antibacterial activity against Staphylococcus aureus (SA), methicillin-resistant Staphylococcus aureus (MRSA), Escherichia coli (EC) and Pseudomonas aeruginosa (PA), including antifugal activity against Candida albicans (CA) by the agar hole diffusion test. The extracts were prepared through macerating at room temperature and hot refluxing procedures. 19 of the 20 extracts showed effects with different potency and their inhibition zone diameters (IZD) ranged from 9 to 27 mm. The extracts from Psychotria henryi Levl and Marsdenia tinctoria R. Br. (maceration and reflux extraction) were the most active against both SA and MRSA, with mean IZDs = 19.7 to 22.0 mm. The anti-SA and MRSA active extracts were further determined for minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC) by serial dilution with a standard broth microdilution method. 12 extracts showed effects on both SA and MRSA strains with MICs/MBCs ranges among 32 to ≥ 1024 / 64 to ≥ 1024 mg/L, respectively. P. henryi, M. tinctoria and Sapium baccatum Roxb also showed inhibition against EC, PA and CA strains, and displayed a broad spectrum of antimicrobial activities. Key words: Chinese herbal, methicillin-resistant Staphylococcus aureus (MRSA), minimum inhibitory concentrations (MIC).