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Abstract
BackgroundOne of the limitations of antibiotic therapy is that even after successful killing of the infecting microorganism, virulence factors may still be present and cause significant damage to the host. Light-activated antimicrobials show potential for the treatment of topical infections; therefore if these agents can also inactivate microbial virulence factors, this would represent an advantage over conventional antibiotic therapy. Staphylococcus aureus produces a wide range of virulence factors that contribute to its success as a pathogen by facilitating colonisation and destruction of host tissues.ResultsIn this study, the ability of the light-activated antimicrobial agent methylene blue in combination with laser light of 665 nm to inactivate staphylococcal virulence factors was assessed. A number of proteinaceous virulence factors were exposed to laser light in the presence of methylene blue and their biological activities re-determined. The activities of V8 protease, α-haemolysin and sphingomyelinase were shown to be inhibited in a dose-dependent manner by exposure to laser light in the presence of methylene blue.ConclusionThese results suggest that photodynamic therapy could reduce the harmful impact of preformed virulence factors on the host.
Highlights
One of the limitations of antibiotic therapy is that even after successful killing of the infecting microorganism, virulence factors may still be present and cause significant damage to the host
These results suggest that photodynamic therapy could reduce the harmful impact of preformed virulence factors on the host
Treatment of EMRSA-16 with 20 μM methylene blue and a laser light dose of 1.93 J/cm2 resulted in an approximate 4-log reduction in viability, corresponding to 99.98% kill
Summary
One of the limitations of antibiotic therapy is that even after successful killing of the infecting microorganism, virulence factors may still be present and cause significant damage to the host. Staphylococcus aureus produces a wide range of virulence factors that contribute to its success as a pathogen by facilitating colonisation and destruction of host tissues. Its success as a human pathogen is highlighted by the fact that despite the development of antibiotic therapy, the frequency of staphylococcal bacteraemias is increasing [2]. S. aureus is the most frequent cause of surgical site infections, accounting for 38% of infections reported in the UK during the period January 2003 to December 2007 [4]. Methicillin-resistant S. aureus (MRSA) accounts for a high proportion of surgical site infections caused by S. aureus, being responsible for 64% of such infections in 2007/ 2008 [4]. The proportion of MRSA isolates from blood cultures taken from cases of bacteraemia in England has risen dramatically from less than 5% in 1990 to around 40% by the end (page number not for citation purposes)
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