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Background  Bletillae Rhizoma, the tuber of  Bletilla striata , has been used in Chinese traditional medicine to treat infectious diseases. Chemical studies indicated that phenanthrene was one of the most important components of the herb, with a broad spectrum of antibiotic activity against Gram-positive bacteria. The objective of this study was to further characterize the antibacterial activity of the phenanthrene fraction from the fibrous root of the pseudobulb of  B. striata .    Methods  The phenanthrene fraction (EF60) from the ethanol extract of fibrous roots of  Bletilla striata  pseudobulbs was isolated using polyamide column chromatography. The antibacterial activity of the fraction was evaluated in vitro using a 96-well microtiter plate and microbroth dilution method. The cytotoxicity of EF60 against mammalian cells was tested by hemolysis and MTT assays.    Results  EF60 was obtained using alcohol extraction and polyamide column chromatography, with a yield of 14.9 g per 1 kg of the fibrous roots of  B. striata . In vitro tests indicated that EF60 was active against all tested strains of  Staphylococcus aureus , including clinical isolates and methicillin-resistant  S. aureus  (MRSA). The minimum inhibitory concentration (MIC) values of EF60 against these pathogens ranged from 8 to 64 μg/mL. Minimum bactericidal concentration tests demonstrated that EF60 was bactericidal against  S. aureus  3304 and ATCC 29213 and was bacteriostatic against  S. aureus  3211, ATCC 25923, and ATCC 43300. Consistently, the time-kill assay indicated that EF60 could completely kill  S. aureus  ATCC 29213 at 2× the MIC within 3 h but could kill less than two logarithmic units of ATCC 43300, even at 4× the MIC within 24 h. The postantibiotic effects (PAE) of EF60 (4× MIC) against strains 29213 and 43300 were 2.0 and 0.38 h, respectively. Further studies indicated that EF60 (160 μg/mL) showed no cytotoxicity against human erythrocytes, and was minimally toxic to Human Umbilical Vein Endothelial Cells with an IC 50  of 75 μg/mL.    Conclusions  Our studies indicated that EF60 is worthy of further investigation as a potential phytotherapeutic agent for treating infections caused by  S. aureus  and MRSA.    Electronic supplementary material  The online version of this article (doi:10.1186/s12906-016-1488-z) contains supplementary material, which is available to authorized users.

The anti-Staphylococcus aureus activity of the phenanthrene fraction from fibrous roots of Bletilla striata