{"status":"ok","message-type":"work","message-version":"1.0.0","message":{"institution":[{"name":"bioRxiv"}],"indexed":{"date-parts":[[2026,7,30]],"date-time":"2026-07-30T10:13:22Z","timestamp":1785406402958,"version":"3.56.0"},"posted":{"date-parts":[[2025,9,24]]},"group-title":"Microbiology","reference-count":37,"publisher":"openRxiv","license":[{"start":{"date-parts":[[2025,9,24]],"date-time":"2025-09-24T00:00:00Z","timestamp":1758672000000},"content-version":"vor","delay-in-days":0,"URL":"https:\/\/www.biorxiv.org\/about\/FAQ#license"}],"funder":[{"award":["AI178152"],"award-info":[{"award-number":["AI178152"]}],"id":[{"id":"https:\/\/ror.org\/01cwqze88","id-type":"ROR","asserted-by":"publisher"}]}],"content-domain":{"domain":[],"crossmark-restriction":false},"short-container-title":[],"accepted":{"date-parts":[[2025,9,24]]},"abstract":"<jats:title>ABSTRACT<\/jats:title>\n                <jats:sec>\n                  <jats:title>Importance<\/jats:title>\n                  <jats:p>Perforated appendicitis is a common and morbid pediatric surgical condition frequently requiring prolonged antibiotic therapy. Adjunctive intraoperative strategies for local antimicrobial therapy are limited, and photodynamic therapy (PDT) may offer a targeted, resistance-independent approach.<\/jats:p>\n                <\/jats:sec>\n                <jats:sec>\n                  <jats:title>Objective<\/jats:title>\n                  <jats:p>To evaluate the feasibility, safety, and preliminary efficacy of laparoscopic methylene blue photodynamic therapy (MB-PDT) for intra-abdominal disinfection in a rabbit model of perforated appendicitis.<\/jats:p>\n                <\/jats:sec>\n                <jats:sec>\n                  <jats:title>Design<\/jats:title>\n                  <jats:p>Experimental preclinical animal study conducted between 2023 and 2025.<\/jats:p>\n                <\/jats:sec>\n                <jats:sec>\n                  <jats:title>Setting<\/jats:title>\n                  <jats:p>Single-center laboratory-based animal research facility affiliated with an academic medical center.<\/jats:p>\n                <\/jats:sec>\n                <jats:sec>\n                  <jats:title>Participants<\/jats:title>\n                  <jats:p>Nineteen New Zealand White rabbits underwent surgically induced perforated appendicitis with peritonitis via appendiceal ligation and electrocautery perforation.<\/jats:p>\n                <\/jats:sec>\n                <jats:sec>\n                  <jats:title>Interventions<\/jats:title>\n                  <jats:p>\n                    Rabbits received laparoscopic MB-PDT (n=9) or control conditions (methylene blue only, no light; n=10) 24 \u2013 40 hours after appendiceal perforation. MB-PDT involved peritoneal lavage with 300 \u00b5g\/mL methylene blue, followed by 665 nm laser illumination to 25 J\/cm\n                    <jats:sup>2<\/jats:sup>\n                    . Peritoneal aspirates were collected before and 24h after intervention. Bacterial burden was quantified, and isolated bacteria were submitted to\n                    <jats:italic>in vitro<\/jats:italic>\n                    PDT. Tissue samples from intraperitoneal organs were collected 24 hours post-intervention.\n                  <\/jats:p>\n                <\/jats:sec>\n                <jats:sec>\n                  <jats:title>Main Outcomes and Measures<\/jats:title>\n                  <jats:p>\n                    Primary outcomes included feasibility of PDT delivery, safety (histologic evidence of off-target injury), and preliminary\n                    <jats:italic>in vivo<\/jats:italic>\n                    efficacy (change in bacterial burden pre-vs. post-intervention). Secondary outcomes included clinical parameter changes and\n                    <jats:italic>in vitro<\/jats:italic>\n                    MB-PDT efficacy.\n                  <\/jats:p>\n                <\/jats:sec>\n                <jats:sec>\n                  <jats:title>Results<\/jats:title>\n                  <jats:p>\n                    Of the 14 rabbits that developed peritonitis, 10 (age 5\u20136 months, weight 3.1\u20133.8 kg) completed follow-up. Laparoscopic MB-PDT delivery was feasible and caused no off-target histologic injury. Bacterial burden increased in MB-PDT animals relative to controls, though not significantly (p=0.18). Post-intervention, body temperature showed a trend toward reduction in MB-PDT animals (\u22120.37 \u00b1 1.32\u00b0C) vs controls (0.26 \u00b1 0.76\u00b0C; p=0.27).\n                    <jats:italic>In vitro<\/jats:italic>\n                    MB-PDT significantly reduced bacterial burden for all tested species (p&lt;0.001), with greater efficacy in Gram-positive bacteria.\n                  <\/jats:p>\n                <\/jats:sec>\n                <jats:sec>\n                  <jats:title>Conclusions and Relevance<\/jats:title>\n                  <jats:p>\n                    Laparoscopic MB-PDT was feasible and safe in a rabbit model of perforated appendicitis, with high\n                    <jats:italic>in vitro<\/jats:italic>\n                    antimicrobial efficacy. Although\n                    <jats:italic>in vivo<\/jats:italic>\n                    bacterial reduction was not demonstrated, these results support further investigation of MB-PDT as a novel intraoperative adjunct for treating intra-abdominal infection.\n                  <\/jats:p>\n                <\/jats:sec>","DOI":"10.1101\/2025.09.24.678338","type":"posted-content","created":{"date-parts":[[2025,9,25]],"date-time":"2025-09-25T03:00:13Z","timestamp":1758769213000},"source":"Crossref","is-referenced-by-count":0,"title":["Intra-Abdominal Photodynamic Therapy in a Rabbit Model of Perforated Appendicitis"],"prefix":"10.64898","author":[{"given":"Timothy M.","family":"Baran","sequence":"first","affiliation":[],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Korry T.","family":"Wirth","sequence":"additional","affiliation":[],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Matthew 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