RecruitingProcedurePathogenesis of Postoperative Infections and Biomarkers for Early Diagnosis of itInfections remain a prevalent complication after major abdominal surgery. The common belief that most surgical site infections (SSIs) following elective surgery with modern antiseptic techniques are due to intraoperative contamination is still not confirmed. Therefore, alternative mechanisms for SSI development, such as the Trojan Horse theory-which suggests that pathogens from distant sites like the gastrointestinal tract may cause postoperative infections-should be explored. This study aims to analyze the preoperative microbiome of surgical patients' gut and oral cavities and assess whether microorganisms found there are present at the infection site. Additionally, this study will investigate a panel of biomarkers for predicting postoperative infections.