Chinese researchers examined the antibiotic potential of phenanthrene, a fraction derived from the tuber of the Chinese ground orchid (Bletilla striata). They reported that phenanthrenes showed significant bactericidal and bacteriostatic effects on several pathogenic strains of Staphylococcus aureus bacteria.
The research was supported by the Zhejiang Chinese Medical University. The outcome was published in the journal BMC Complementary and Alternative Medicine.
Phenanthrene was isolated from an ethanol extract made from the tubers of Chinese ground orchid plants. The fraction was tested for its antibacterial activity on different Staphylococcus strains as well as its potential toxic effects on mammalian cells.
In the antibacterial tests, phenanthrene demonstrated significant activity against all of the Staphylococcus strains. This included clinical isolates and methicillin-resistant S. aureus (MRSA) strain.
Depending on the strain, the minimum amount of phenanthrene needed to inhibit bacterial growth ranged from a low of eight micrograms per milliliter (mg/mL) to a high of 64 mg/mL.
Minimum bactericidal concentrations of the extract were lethal to the 3304 and ATCC 29213 strains. Against the 3211, ATCC 25923, and ATCC 43300 strains, phenanthrene was merely bacteriostatic.
In the cytotoxicity test, 160 micrograms/milliliter of phenanthrene did not appear to be cytotoxic on human red blood cells. It was slightly toxic to Human Umbilical Vein Endothelial Cells (HUVEC) at 75 micrograms/milliliter.
Their findings led the researchers to conclude that the phenanthrene fraction in the Chinese ground orchid has significant promise as a natural treatment for infections caused by pathogenic Staphylococcus bacteria, especially the drug-resistant strain.