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Helicobacter pylori infection in the stomach causes peptic ulcers and gastric cancer. Antibiotic therapy leads to 80%-eradication but has side effects and increasing antibiotic resistance is becoming problematic. Antimicrobial photodynamic therapy has been studied as an alternative approach to killing the bacteria in the stomach lining. In vitro photoinactivation with several photosensitizers has been reported, and an ex vivo study in ferret stomach samples, and a human clinical trial using ALA-PDT have been published. We discovered that H. pylori is susceptible to killing by visible light without added PS. Violet light is most effective (six logs10 of kill by 20-J/cm2 and both the bacterial pellets and culture supernatant accumulate significant amounts of the photoactive porphyrins, coproporphyrin and protoporphyrin. A Phase I clinical trial included patients with dyspepsia and HP infection. At endoscopy a 1-cm2 site in the pyloric antrum was exposed to 405-nm violet light (140-mW/cm2, 40-J), via a diode laser-coupled optical fiber. Biopsies were taken from the control and illuminated sites and average killing of >90% of bacteria. A second clinical trial used whole-stomach illumination with 405-nm light at endoscopy. Quantitative culture from biopsies showed the largest reduction (2 logs) in bacterial load was in the antrum, followed by the body and fundus. There was a correlation between log reduction and initial bacterial load in the antrum.

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