Photodynamic inactivation of bacteria to decolonize meticillin-resistant Staphylococcus aureus from human skin.

BACKGROUND: To prevent infections that arise from the skin surface it is necessary to decolonize human skin prior to any proposed treatment or surgical intervention. Photodynamic inactivation of bacteria (PIB) uses cationic photosensitizers that attach to the surface of bacteria, generate reactive oxygen species on light irradiation and thereby kill bacteria via oxidative mechanisms. OBJECTIVES: To evaluate the potential and the safety of PIB for decolonization of bacteria from skin. METHODS: PIB with the new photosensitizer SAPYR [2-((4-pyridinyl)methyl)-1H-phenalen-1-one chloride] was initially tested against different bacterial species in vitro. Then, ex vivo porcine skin samples were used as a model for decolonization of different bacteria species. The numbers of viable bacteria were quantified and the mitochondrial activity of skin cells was histologically analysed (using nitroblue tetrazolium chloride, NBTC). The same procedure was performed for human skin and meticillin-resistant Staphylococcus aureus (MRSA). RESULTS: The in vitro studies showed a 5 log10 reduction of all tested bacterial species. On ex vivo porcine skin samples, PIB reduced the viability of all tested bacterial species by at least 3 log10 steps. On human skin samples ex vivo, PIB reduced the number of viable MRSA by maximal 4·4 log10 steps (1000 µmol L-1 SAPYR, incubation time 10 min, 60 J cm-2 ). NBTC staining showed normal mitochondrial activity in skin cells after all PIB modalities. CONCLUSIONS: The results of this study show that PIB can effectively and safely kill bacteria like MRSA on the skin surface and might have the potential of skin decolonization in vivo.

Novel photodynamic coating reduces the bioburden on near-patient surfaces thereby reducing the risk for onward pathogen transmission: a field study in two hospitals.

BACKGROUND: Near-patient surfaces are recognized as a source for hospital-acquired infections. Such surfaces act as reservoirs for microbial contamination by which pathogens can be transmitted from colonized or infected patients to susceptible patients. Routine disinfection of surfaces only results in a temporal elimination of pathogens, and recontamination inevitably occurs shortly between disinfections. AIM: A novel antimicrobial coating based on photodynamics was tested under laboratory conditions and subsequently in a field study in two hospitals under real-life conditions. METHODS: Identical surfaces received a photodynamic or control coating. Bacterial counts [colony-forming units (cfu)/cm2) were assessed regularly for up to 6 months. FINDINGS: The laboratory study revealed a mean reduction of several human pathogens of up to 4.0 ± 0.3 log10. The field study in near-patient environments demonstrated mean bacterial values of 6.1 ± 24.7 cfu/cm2 on all control coatings. Photodynamic coatings showed a significantly lower mean value of 1.9 ± 2.8 cfu/cm2 (P<0.001). When considering benchmarks of 2.5 cfu/cm2 or 5 cfu/cm2, the relative risk for high bacterial counts on surfaces was reduced by 48% (odds ratio 0.38, P<0.001) or 67% (odds ratio 0.27, P<0.001), respectively. CONCLUSION: Photodynamic coatings provide a significant and lasting reduction of bacterial counts on near-patient surfaces, particularly for high bacterial loads, in addition to routine hygiene. The promising results of this proof-of-concept study highlight the need for further studies to determine how this novel technology is correlated with the frequency of hospital-acquired infections.