Abstract
Evidence has shown that environmental surfaces play an important role in the transmission of nosocomial pathogens. Deploying antimicrobial surfaces in hospital wards could reduce the role environmental surfaces play as reservoirs for pathogens. Herein we show a significant reduction in viable counts of Staphylococcus epidermidis, Saccharomyces cerevisiae, and MS2 Bacteriophage after light treatment of a medical grade silicone incorporating crystal violet, methylene blue and 2 nm gold nanoparticles. Furthermore, a migration assay demonstrated that in the presence of light, growth of the fungus-like organism Pythium ultimum and the filamentous fungus Botrytis cinerea was inhibited. Atomic Force Microscopy showed significant alterations to the surface of S. epidermidis, and electron microscopy showed cellular aggregates connected by discrete surface linkages. We have therefore demonstrated that the embedded surface has a broad antimicrobial activity under white light and that the surface treatment causes bacterial envelope damage and cell aggregation.
Highlights
Work has previously been carried out[5,6] to incorporate a combination of two photosensitizers and nanogold into a soft polymer to be employed in hospital touch surfaces (e.g mobile phone covers, computer keyboards and hand dryers) to reduce nosocomial infection transmission
It is demonstrated that the incorporation of the methylene blue, crystal violet, and the gold nanoparticles did not alter the topography of the silicone
After air-drying and washing the polymers were exposed to an aqueous crystal violet solution such that strong uptake of the dye was achieved on the polymer surfaces, for high surface generation of reactive oxygen species (ROS) in the environs of contaminating microorganisms[7]
Summary
Work has previously been carried out[5,6] to incorporate a combination of two photosensitizers and nanogold into a soft polymer to be employed in hospital touch surfaces (e.g mobile phone covers, computer keyboards and hand dryers) to reduce nosocomial infection transmission. The photosensitizer molecule is excited, with light of a wavelength at its absorbance peak, to a singlet state. The Type I pathway involves electron transfer between the triplet state photosensitizer molecule and nearby molecules, such as water or biological molecules, to produce a wide range of reactive oxygen species (ROS) and radical ions. The Type II process involves energy transfer between the triplet state photosensitizer and molecular oxygen, which has a triplet ground state, resulting in the generation highly reactive singlet oxygen. We present the assessment of the antimicrobial activity of the light-activated methylene blue-crystal violet-nanogold silicone surface tested against unicellular microorganisms: Staphylococcus epidermidis, Saccharomyces cerevisiae, and MS2 Bacteriophage as model organisms for bacteria, yeasts, and viruses, respectively. Microscopy and spectrometry were used to determine whether the generation of exogenous ROS by the photosensitizer-based surface caused damage to the bacterial cell envelope, as proposed by Dahl, et al.[10]
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