Laparoscopic Methylene Blue Photodynamic Therapy for Intraabdominal Infection: A Preclinical Feasibility Study in a
Timothy M Baran1,2, Korry T Wirth2,3, Matthew M Byrne4
1Department of Imaging Sciences, University of Rochester Medical Center, Rochester, New York, USA.
Objectives:
Perforated appendicitis commonly results in intra-abdominal infection requiring prolonged antibiotic therapy. Intraoperative antimicrobial adjuncts are limited, and photodynamic therapy (PDT) may provide a targeted, resistance-independent approach. This study evaluated the feasibility, safety, and preliminary antimicrobial effects of laparoscopic methylene blue photodynamic therapy (MB-PDT) for intra-abdominal disinfection in a rabbit model of perforated appendicitis.
Materials And Methods:
New Zealand White rabbits (n = 19) underwent surgically induced perforated appendicitis via appendiceal ligation and electrocautery perforation. Animals subsequently received laparoscopic MB-PDT (n = 9) or control treatment (methylene blue lavage without laser illumination; n = 10) 24-40 h after perforation. MB-PDT consisted of peritoneal lavage with methylene blue (300 µg/mL) followed by 665-nm laser illumination at 20 mW/cm2 to a fluence of 25 J/cm2. Peritoneal aspirates were obtained before and 24 h after intervention to quantify bacterial burden. In vitro PDT was evaluated in isolated organisms. Intraperitoneal organs were assessed histologically for off-target effects. Primary outcomes were feasibility, safety, and in vivo change in bacterial burden. Secondary outcomes included clinical parameter changes and in vitro efficacy.
Results:
Fourteen rabbits developed peritonitis, and 10 animals completed follow-up (PDT n = 7, control n = 3). Laparoscopic MB-PDT delivery was technically feasible and no histologic evidence of off-target photodynamic injury to abdominal organs was identified. Changes in bacterial burden were not significantly different between MB-PDT and control animals (p = 0.18). Body temperature showed a non-significant trend toward reduction following MB-PDT (-0.37°C ± 1.32°C) compared with controls (0.26°C ± 0.76°C; p = 0.27). In vitro MB-PDT produced significant reductions in bacterial burden across all isolated species (p < 0.001), with the most resistant Gram-positive isolate, Enterococcus faecalis, demonstrating greater susceptibility than Gram-negative species.
Conclusion:
Laparoscopic MB-PDT was technically feasible and safe in a rabbit model of perforated appendicitis. Although a reduction in bacterial burden was not observed in vivo, MB-PDT produced strong antimicrobial activity in vitro against all bacterial species isolated from infected animals. These findings establish a preclinical technical platform for intra-abdominal MB-PDT and highlight the importance of optimized light-delivery strategies for future translational studies.
