Spontaneous Bacterial Peritonitis in Advanced Cirrhosis: Diagnosis by Tm Mapping and Inflammatory Profiles of Extracellular Vesicles

Background/Objectives: Ascites is a major complication in patients with decompensated cirrhosis. Spontaneous bacterial peritonitis (SBP), an infection of the ascitic fluid, is a life-threatening condition in patients with cirrhosis. This study aimed to assess the utility of Tm mapping, a novel high-efficacy method for bacterial detection and quantification, in the early diagnosis of SBP and its pathogenesis. Methods: Ascitic fluid samples from 29 patients with cirrhosis were analyzed using Tm mapping for bacterial identification. Inflammatory cytokine and pathogen-associated molecular pattern levels in ascitic fluid were measured and correlated with SBP pathophysiology. Additionally, the role of ascitic macrophages was investigated in vitro. Results: Tm mapping detected bacteria more effectively than conventional culture methods. In samples where bacteria were identified, ascitic interleukin (IL)-6 levels were elevated. A positive correlation was observed between extracellular vesicle (EV) levels and IL-6, suggesting a role for EVs in peritoneal inflammation. Furthermore, EVs derived from Gram-negative bacteria induced M1 macrophage differentiation via the signal transducer and activator of transcription 1 signaling pathway. Conclusions: Tm mapping is a valuable tool for the early detection of bacteria in ascitic fluid. Additionally, EVs promote M1 macrophage differentiation, implicating them in the pathogenesis of cirrhotic complications, including SBP.