aureus has been demonstrated in a number of infection models such as mastitis [23] and pneumonia [24]. It has also been proposed that α-haemolysin may play a role in colonisation of epithelia by attenuating bacterial clearance from the epithelial surface [25]; this could therefore be of relevance see more to the decontamination of nasal epithelia using PDT. In addition,

α-haemolysin has immunomodulatory properties, notably its ability to trigger the release of pro-inflammatory cytokines such as interleukin-1β [26]; thus inactivation of α-haemolysin by PDT may also protect against harmful inflammatory processes as well as eliminating infecting organisms. The treatment of S. aureus sphingomyelinase with laser light and methylene blue resulted in a significant, dose-dependent reduction in the

enzyme’s activity. Laser light alone also appeared to reduce the activity of sphingomyelinase; however this was found to be not statistically significant. Irradiation of sphingomyelinase with 1.93 J/cm2 laser light in the presence of the highest concentration of methylene blue tested (20 μM) achieved a highly significant reduction in the activity of the enzyme (76%), which was comparable to CH5424802 mouse the reduction in activity observed for the V8 protease when irradiated for the same time period. This reduction in activity was increased to 92% after irradiation of the enzyme for 5 minutes in the presence of 20 μM methylene blue. Production of sphingomyelinase (β-haemolysin) is thought to be of importance in severe, chronic skin infections, and strains of S. aureus producing high levels of this enzyme have been shown to cause more intense skin lesions than low-producing strains [27]. Inactivation of these toxins may therefore

be of notable relevance to the treatment of superficial staphylococcal skin infections. Sphingomyelinase has recently been shown to kill BIRB 796 mouse proliferating T lymphocytes, suggesting a role for this toxin in evasion of the host immune response [28]; hence inactivation of sphingomyelinase by PDT could also reduce the immunomodulatory properties of S. aureus. The photodynamic inactivation of α-haemolysin and sphingomyelinase was shown to be unaffected by the presence of human serum at concentrations resembling the protein content of an acute wound[29], indicating that photodynamic Ureohydrolase therapy may be effective in inactivating these virulence factors in vivo. Together with the data showing that PDT using methylene blue and 665 nm laser light is effective against a methicillin-resistant strain of S. aureus, this supports the potential of PDT as a treatment for superficial staphylococcal infections. The precise mechanism of inhibition of these virulence factors has not yet been determined; however it is possible that the reactive oxygen species formed during photosensitisation can oxidise proteins, thereby disrupting their function [13].