Helicobacter pylori inhibition by antimicrobial photodynamic therapy of methylene blue and porphyrin.

Helicobacter pylori is the pathogen responsible for peptic ulcers and gastritis, affecting half of the population around the world. The infection of H. pylori is commonly treated with a combination of antibiotics, but the effectiveness is decreasing due to the rising multidrug resistance in recent years. Antimicrobial photodynamic therapy is a promising alternative for H. pylori eradication, where light irradiation activates photosensitizer to produce reactive oxygen species in situ, thus inducing cell death through irreversible oxidative damage. Methylene blue is widely used as a coloring agent for chromoendoscopy and also proved to be an effective photosensitizer against bacteria, fungi, viruses, and cancer cells. Additionally, photosensitizer porphyrin is naturally produced and accumulated within H. pylori cells. Here, we investigated the inhibitory effects of photosensitizer methylene blue and porphyrin against H. pylori free-swimming cells and sessile biofilms. Additionally, we used suckling pig as an animal model to determine the efficiency of antimicrobial photodynamic therapy in the treatment of H. pylori infection. Results showed that free-swimming H. pylori was eliminated effectively, either by 10 µM of methylene blue under the light irradiation of 660 nm or by endogenous porphyrin activated under the light irradiation of 410 nm. In contrast, H. pylori biofilms exhibited resistance. Moreover, in vivo experiments showed that antimicrobial photodynamic therapy could inhibit H. pylori in the stomach of sucking pigs, but occasional recurrent infections were present.IMPORTANCEThe rising prevalence of multidrug-resistant Helicobacter pylori severely compromises conventional antibiotic therapies, necessitating novel treatment strategies. Antimicrobial photodynamic therapy (aPDT) offers a promising alternative by using light-activated reactive oxygen species to kill bacteria. Here, we show that both exogenous methylene blue and endogenous porphyrin can effectively eliminate free-swimming H. pylori under light irradiation. Using a physiologically relevant suckling pig model, we demonstrate that aPDT reduces gastric H. pylori in vivo, although recurrent infection was observed. This study provides critical preclinical evidence for aPDT as a potential adjunctive strategy in the treatment of H. pylori infection, while highlighting the key challenges of biofilm resistance.