Sensitization of Staphylococcus aureus to killing by low-power laser light.

Staphylococcus aureus is the aetiological agent of a wide range of infections, both nosocomial and community-acquired, and topically-applied antimicrobials are often used for their prevention, control and treatment; for example, isopropanol/hexachlorophane is applied to the umbilicus of neonates to prevent colonization (Watkinson & Dyas, 1992), mupirocin is used to eliminate nasal carriage (Casewell & Hill, 1986) and fusidic acid is used to treat skin infections (Greenwood, 1989). However, the development of resistance to many of these topical agents has been a cause for concern (Grosserode & Wenzel, 1991) and emphasizes the need to identify new techniques to eradicate 5. aureus from infected wounds and carriage sites. Malignant mammalian cells are killed by exposure to low dosages of laser light when they have been pre-treated with a photosensitizing agent, and this is the basis for photodynamic therapy of tumours (Dougherty, Potter & Bellnier, 1990). A number of studies have demonstrated that bacteria can also be sensitized to killing by low-power laser light which, itself, is not bactericidal (MacMillan, Maxwell & Chichester, 1966; Wilson, 1993); this antimicrobial activity is thought to be mediated by singlet oxygen and free radicals generated by the photoactivated sensitizer (Spikes & Jori, 1987; Malik, Hanania & Nitzan, 1990). The purpose of this investigation was to determine whether this strategy could be used to kill S. aureus in vitro.