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LED-Based In Vitro Screening for Assessing Photoactivable Molecules in Bacterial Photodynamic Inactivation

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Hypericin-mediated photodynamic antimicrobial effect on clinically isolated pathogens.

Christine M N Yow¹, Hi M Tang, Ellie S M Chu

¹Section of Medical Laboratory Science, Department of Health Technology & Informatics, Hong Kong Polytechnic University, Kowlong, HKSAR, China. christine.yow@inet.polyu.edu.hk

Photochemistry and Photobiology

|January 12, 2012

Summary

Hypericin photodynamic therapy effectively kills Staphylococcus aureus but not Escherichia coli. Differences in bacterial cell structure impact hypericin uptake and antimicrobial efficacy.

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Area of Science:

Photodynamic antimicrobial chemotherapy
Bacteriology
Cellular microbiology

Background:

Antimicrobial resistance is a growing global health concern.
Photodynamic antimicrobial chemotherapy (PACT) offers a potential alternative treatment strategy.
Hypericin, a natural photosensitizer, has demonstrated antimicrobial properties.

Purpose of the Study:

To evaluate the photodynamic antimicrobial effect of hypericin against clinical isolates of Staphylococcus aureus and Escherichia coli.
To investigate the influence of bacterial cellular structure on hypericin-mediated photodynamic killing.

Main Methods:

Bacterial cells were incubated with varying concentrations of hypericin.
Cells were exposed to specific light irradiation wavelengths and doses.
Cell survival, hypericin uptake, and cell membrane damage were quantified.

Main Results:

Hypericin-mediated photodynamic therapy achieved significant killing (>6 log reduction) of both methicillin-sensitive and -resistant Staphylococcus aureus.
Photodynamic treatment with hypericin showed minimal efficacy (<0.2 log reduction) against Escherichia coli.
Differential cellular uptake of hypericin, influenced by cell wall and membrane structures, correlated with antimicrobial effectiveness.

Conclusions:

Hypericin-PACT is a promising strategy for targeting Gram-positive bacteria like Staphylococcus aureus.
The distinct cell envelope structures of Gram-negative bacteria, such as Escherichia coli, limit hypericin uptake and photodynamic efficacy.
Further research into optimizing hypericin delivery or combination therapies may enhance its effectiveness against a broader spectrum of bacteria.