Extracts from St John's Wort and their antimicrobial activity

Area of Science:

• Pharmacology
• Natural Products Chemistry
• Microbiology

Background:

• *Hypericum perforatum* (St. John's Wort) is a medicinal plant with a history of traditional use.
• Its potential antimicrobial properties warrant scientific investigation to validate traditional applications.
• Understanding the active compounds responsible for antimicrobial effects is crucial for drug development.

Purpose of the Study:

• To evaluate the antimicrobial activity of various *Hypericum perforatum* extracts.
• To identify the specific compounds within the most active extract responsible for antimicrobial effects.
• To determine the efficacy of isolated compounds against selected microorganisms.

Main Methods:

• Extraction of *Hypericum perforatum* aerial parts using different solvents (Methanol, petroleum ether, chloroform, ethyl acetate).
• Antimicrobial susceptibility testing of extracts against Gram-positive and Gram-negative bacteria.
• High-Performance Liquid Chromatography (HPLC) analysis to identify major constituents of the active extract.
• Testing of isolated compounds (hypericin, hyperforin, flavonoids) for antimicrobial activity.

Main Results:

• Ethyl acetate extract exhibited the most potent antimicrobial activity.
• Growth inhibition was observed exclusively against Gram-positive bacteria, notably *Bacillus subtilis* and *Bacillus cereus*.
• HPLC analysis identified flavonoids, hypericins, and hyperforins as main constituents of the ethyl acetate extract.
• Pure hypericin and hyperforin (and its salt) demonstrated significant growth inhibition, while flavonoids showed no activity.

Conclusions:

• The antimicrobial activity of *Hypericum perforatum* is primarily attributed to hypericin and hyperforin.
• These compounds are effective against specific Gram-positive bacteria.
• Flavonoids present in the extract do not contribute significantly to the observed antimicrobial effects.