Omar, G.S.M.; (2010) Killing of organisms responsible for wound infections using a light-activated antimicrobial agent. Doctoral thesis , UCL (University College London).

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Abstract

Infected wounds are a major cause of hospital-acquired infections and these are difficult to treat due to the emergence of antibiotic-resistant bacteria. This project is concerned with evaluating a novel antimicrobial approach involving the photosensitizer indocyanine green (ICG) which generates reactive oxygen species when irradiated with near-infrared (NIR) light which enables good tissue penetration. The photo-susceptibility of common wound-infecting organisms to ICG coupled with NIR-light was investigated. All species were susceptible to killing. ICG at a concentration of 25 μg/mL enabled the killing of the Gram-positive species (Staphylococcus aureus and Streptococcus pyogenes), higher concentrations (100-200μg/mL) were necessary to achieve substantial kills of the Gram-negative species (Pseudomonas aeruginosa and Escherichia coli). Both high and low fluences were able to kill 99.999% of the Gram-positive bacteria. High fluence irradiation was necessary to kill 99.99% of the Gram-negative bacteria. The pulsed-mode of irradiation was as effective as the continuous-mode for killing the Gram-positive species. Yet only the continuous-mode of irradiation was able to kill P. aeruginosa. Biofilms of Staph. aureus and P. aeruginosa were susceptible to disruption and killing by ICG-photosensitization. A significant enhancement of lethal photosensitization of Staph. aureus was achievable using gold-nanoparticles and antioxidants. Significant kills (>99%) were achieved in the presence of serum and 100 μg/mL ICG. A low oxygen concentration reduced the kills to 96.77% and 71.62% for Staph. aureus and Strep. pyogenes respectively. Mechanistic studies revealed that killing was mediated mainly by reactive-oxygen species. In vivo studies in mice showed that ICG and continuous-NIR light could achieve kills of 96%, 93% and 78-91% for P. aeruginosa, Strep. pyogenes and Staph. aureus respectively. The results of these in vitro and in vivo studies imply that ICG-PDT could be an effective means of decreasing the microbial burden in wounds.

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