Antibiotic Resistance Pattern and Surgical Outcome in Complicated Intra-Abdominal Infections Due to Colorectal Perforation

<b>Background:</b> Intra-abdominal infections (IAIs) are one of the leading causes of non-traumatic death in emergency surgery units. The appropriateness of empirical antibiotic therapy is fundamental for outcomes and for limiting the spread of resistance. This study aimed to assess the epidemiology and antibiotic resistance patterns of microorganisms recovered from complicated intra-abdominal infections due to colorectal perforation at an Italian University Hospital during a nine-year period. <b>Methods</b>: This study evaluated a cohort of patients subjected to emergency surgery for colonic perforation with collected intrabdominal fluid samples from 2015 to 2024. Patterns of isolated bacteria and antibiotic resistance status were collected and correlated to patient outcomes. <b>Results</b>: 321 patients were enrolled; the average age was 70.2 years. The main diagnoses were complicated diverticulitis (58%), colorectal carcinoma perforation (18%), and acute intestinal ischemia (24%). 80.4% were immunocompromised; average hospital stay (HLOS) was 15.6 days; 60.1% developed postoperative complications. Microbiological cultures were available for 111 patients: 56.7% had mono-microbial infections and 43.3% multi-microbial infections. 53 antibiotics and 9 antifungals were tested, with resistance rates exceeding 20% for many pathogens. Multivariate analyses showed that documented IAIs are associated with longer postoperative hospital stays (p 0.003 CR 8.075) but not with patient mortality (p 0.031). Prolonged HLOS was more commonly observed in patients with polymicrobial infections or infections caused by multi-drug-resistant organisms (p 0.03; p 0.003). <b>Conclusions</b>: Microbiological characteristics of isolated bacteria do not directly influence mortality; however, the presence of polymicrobial infections and resistant pathogens directly affects the duration of hospitalization and often leads to the development of chronic disease conditions.