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ttaching an antimicrobial drug, which is activated by light, to a peptide that binds to bacteria and stops them making toxins, resulted in a treatment that was highly effective at killing the superbug, methicillin-resistant Staphylococcus aureus or commonly known as MRSA.

Miss Linda Dekker and colleagues from the UCL Eastman Dental Institute, University College London presented the work to the Society for General Microbiology's meeting at Harrogate April 1.

Photodynamic therapy uses antimicrobial agents, in this case tin chlorin e6 (SnCe6), which produce free radicals and an unstable form of oxygen called singlet oxygen when they are exposed to light at the right wavelength. These damage and kill bacteria. To improve the effectiveness of treatment and avoid damage to human cells, the drug was targeted to MRSA by attaching it to a peptide, RNAIII inhibiting peptide (RIP) that binds to a molecular receptor on the bacterium's surface.

What exactly is Photodynamic therapy?

Photodynamic therapy (PDT) is a treatment that uses a drug, called a photosensitizer or photosensitizing agent, and a particular type of light. When photosensitizers are exposed to a specific wavelength of light, they produce a form of oxygen that kills nearby cells (1, 2, 3).

Each photosensitizer is activated by light of a specific wavelength (3, 4). This wavelength determines how far the light can travel into the body (3, 5). Thus, doctors use specific photosensitizers and wavelengths of light to treat different areas of the body with PDT.

How effective was the Treatment?

99.97% of 10 million MRSA cells were killed using this new combination, which was 1000 times more effective at killing MRSA compared to the commercially available SnCe6 when the same quantity is used. In addition to being far more effective at killing the bacteria, the new drug has the potential to prevent bacteria from producing tissue-damaging toxins; the mechanism of killing also means that it is very unlikely that bacteria can develop resistance to this treatment.

"The results from laboratory studies are very encouraging and indicate that this technique might be effective at treating topical infections such as wound and burn infections," said Ms Dekker, "This work will require in vivo trials before it can be used. Due to the growing resistance of many organisms to antibiotics, this approach may be the only one available for use against microbes resistant to all known antibiotics".

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