aureus, which we found to have an 8-fold increase in resistance

to the aminoglycoside kanamycin. Our results demonstrate that the combination of methylene blue and laser light of 665 nm effectively kills S. aureus SCVs, suggesting that photodynamic therapy could be a promising alternative therapy for SCV infections. Selection for SCVs and development of resistance are unlikely due to the non-specific mechanism of action of photodynamic therapy, representing an advantage over conventional antibiotic treatment. One potential limitation to the effectiveness of photodynamic therapy is that in some infections SCVs enter the cytoplasm of host cells [3]. In such cases it is likely that higher photodynamic therapy doses would be required resulting in some collateral damage to host tissue. One possible way to overcome this problem would be to develop photosensitisers that target the intracellular bacteria specifically. Photodynamic therapy has Cyclosporin A been proposed for the decontamination of the anterior nares in cases of MRSA carriage [6, 8, 9]. Cases of infections associated with concomitant colonisation of the anterior nares by S. aureus small colony variants have been reported in the literature [10–12]; therefore, photodynamic therapy may also be of use as a

decontamination strategy in cases where the anterior nares represent a reservoir of SCVs. Conclusion In conclusion, we propose that AZD1480 datasheet photodynamic therapy has potential for use in the treatment of superficial infections by SCVs of S. aureus and for nasal decolonisation. Methods The S. aureus strains used were the laboratory strain 8325–4 and an isogenic

mutant, D1324, disrupted in menD[13], (a gift from Professor Richard Proctor), and LS-1 and its isogenic mutant disrupted in hemB[14]. S. aureus was maintained by subculture on blood agar (Oxoid Ltd, UK) incubated aerobically at 37°C. For experimental purposes, bacteria were inoculated into Brain Heart Infusion broth and cultured aerobically Resveratrol for 16 hrs at 37°C, with shaking at 200 rpm. Cultures were then centrifuged and resuspended in an equal volume of PBS and the optical density adjusted to 0.05 at 600 nm, corresponding to approximately 1 × 107 colony forming units (CFU) per mL. Methylene blue (C16H18ClN3S.3H2O) and all other reagents were purchased from Sigma-Aldrich (UK). The MIC of kanamycin was determined according to the CLSI microbroth dilution. A Periowave™ diode laser (Ondine Biomedical Inc., Canada), which emits light with a wavelength of 665 nm was used Compound C research buy throughout the study. The power output of the laser was 73 mW and the beam diameter was 1.7 cm. The laser system was set up so that the laser beam covered the entire well of a microtitre plate in which experiments were performed. To examine the effect of photosensitiser concentration on the photodynamic killing of S. aureus SCVs, methylene blue was diluted in PBS to give final concentrations of 1, 5, 10 and 20 μM.