According to the Revised Atlanta Classification, walled-off pancreatic necrosis (WOPN) is a late complication of acute pancreatitis, diagnosed >4 weeks after disease onset. Up to 40% of WOPN cases develop secondary infections, which significantly worsen clinical outcomes and increase mortality up to five-fold compared with sterile necrosis. While endoscopic drainage is the preferred treatment, data on the microbiological characteristics of infected WOPN remain limited.

This study aims to characterise the microbial pathogens and their antibiotic resistance patterns in patients undergoing endoscopic stent placement for suspected infected WOPN at a single tertiary care centre the aim of this study is to describe the microbiological profile in infected WOPN. Secondary objectives were to assess antimicrobial resistance patterns, evaluate the effectiveness of empiric antibiotic therapy, and document therapy modifications.

Between October 2021 and October 2025, we performed 3337 endoscopic procedures, including 1705 EUS examinations. During this period, a total of 75 WOPN cases were identified, comprising 40 LAMS insertions, 11 conventional plastic stent insertions, and 24 cases of spontaneous regression.

This retrospective analysis included 51 patients with WOPN who underwent EUS placement of either a plastic or a metal stent. Samples from the WOPN cavity and blood cultures were obtained and sent for microbiological evaluation. We recorded the isolated organisms, resistance profiles, and corresponding antimicrobial therapies

Among 51 patients, 37 had infected WOPN (72.5%; median age 57 [42-69], 32.4% female) and 14 had sterile WOPN (27.5%; median age 64 [54.8-73], 57.1% female). Polymicrobial infection was present in 35/37 infected cases (94.6%), while the remaining two patients had monomicrobial infection. The most frequently isolated organisms included Enterococcus spp. (56.75%), Klebsiella spp. (45.9%), and Pseudomonas spp. (43.2%). Fungal organisms, predominantly Candida spp., were identified in 19 patients (51.3%).

Empiric imipenem was administered to 19 patients (51.3%), with therapy modification required in 16 (84.2%), including 13 modifications due to confirmed imipenem resistance (68%). Overall, imipenem resistance was detected in 24 out of the 37 infected cases (64.8%), and antibiotic modification was required in 19 patients (51.3%).

This study highlights the high rates of bacterial and fungal infections in WOPN, as well as the high prevalence of imipenem resistance, underscoring the need to recognise pathogen profiles to improve treatment protocols and strengthen antimicrobial stewardship in managing necrotising pancreatitis.