Abstract:

[Objective] This study was conducted to screen the Chinese medicinal herbs that have antibacterial and bactericidal actions against Rhodococcus equi （R. equi）. [Method] The aqueous extracts from each of the 8 kinds of Chinese medicinal herbs including Coptis chinensis, Scutellaria baicalensis, Ficus hirta, Houttuynia cordata, Platycladus orientalis, Forsythia suspensa, Lonicera japonica and Isatis tinctoria were prepared, respectively. The minimum inhibitory concentration （MIC） and minimum bactericidal concentration （MBC） of the aqueous extracts from the Chinese medicinal herbs against reference strain 103S and clinical isolates of R. equi were determined using broth micro-dilution method and spread-plate method, respectively. [Result] The antibacterial and bactericidal actions of the aqueous extracts from different Chinese medicinal herbs against R. equi varied, and Coptis chinensis, Platycladus orientalis and Forsythia suspensa had significantly （P<0.05） better performance than the others. The use of different combinations of the aqueous extracts from Coptis chinensis, Platycladus orientalis and Forsythia suspensa exhibited stronger antibacterial and bactericidal actions against R. equi than their single use. The combinative use of Coptis chinensis and Forsythia suspensa showed an additive effect. [Conclusion] The Chinese medicinal herbs such as Coptis chinensis show antibacterial and bactericidal actions against R. equi, and the combinative use of these herbs have better performance than their single use, suggesting that these herbs have potential to be effective therapeutic drugs against infections caused by R. equi and even by other antimicrobial-resistant pathogens.

Key words: Rhodococcus equi, Chinese medicinal herb, minimum inhibitory concentration, minimum bactericidal concentration