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Extracts from St John's Wort and their antimicrobial activity
P Avato1, F Raffo, G Guglielmi
1Dipartimento Farmaco-Chimico, Bari, Italy. avato@farmchim.uniba.it
Abstract:
In an effort to carry out a more in-depth investigation on the antimicrobial properties of H. perforatum, we have assayed different extracts (MeOH; petroleum ether; CHCl(3) and EtOAc) from the aerial parts of the plant against selected microorganisms. Growth inhibition was observed only for Gram-positive bacteria, B. subtilis and B. cereus being the most susceptible to the tested drugs. The Hypericum extract obtained with EtOAc was the most active. The main constituents of this extract, as determined by HPLC analysis, were flavonoids, hypericins and hyperforins. Incubation of the selected microorganisms with the pure chemicals resulted in a significant inhibition of their growth by hypericin, hyperforin and its stable dicyclohexilammonium salt. Flavonoids appeared inactive at all.
Insights
This study investigated the antimicrobial activity of *Hypericum perforatum* extracts. The ethyl acetate extract showed significant antibacterial effects against Gram-positive bacteria, primarily due to hypericin and hyperforin.
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.
