Purpose. To investigate the microbiological spectrum and antibiotic resistance profiles of aerobic pathogens causing complicated intra-abdominal infections in patients treated at a surgical hospital in a northern industrial region. Materials and methods. A prospective single-center observational study included 75 patients with complicated intra-abdominal infections treated in a surgical hospital. Intraoperative specimens were collected directly from the infectious focus. Peritoneal exudate, purulent material, and tissue samples were used as biological material. Etiologically significant microorganisms were isolated in 68 patients. Antimicrobial susceptibility was determined by the disk diffusion method on Mueller-Hinton agar in accordance with national and international recommendations. To strengthen the analytical component, a conditional comparative statistical analysis of antibiotic resistance in the key gram-negative pathogens was performed using reconstructed absolute values derived from the original percentage data. Pearson's chi-square test and Fisher's exact test were used to compare proportions. Statistical significance was set at p < 0.05. Results. Etiologically significant microorganisms were isolated in 90.7% of the examined patients. Escherichia coli predominated in the pathogen structure at 47.1%, followed by Klebsiella spp. at 26.5%, Enterococcus spp. at 23.5%, Proteus spp. at 16.2%, and Pseudomonas aeruginosa at 11.8%. Salmonella spp. at 10.3% and Candida spp. at 7.4% were identified less frequently. Klebsiella spp. showed statistically significantly higher resistance than E. coli to ampicillin/amoxiclav (100.0% vs 34.4%; p < 0.001), third- and fourth-generation cephalosporins (94.4% vs 40.6%; p < 0.001), fluoroquinolones (94.4% vs 40.6%; p < 0.001), and aminoglycosides (94.4% vs 50.0%; p = 0.002). Carbapenems retained high activity against the key gram-negative pathogens. Conclusion. The local microbiological profile of complicated intra-abdominal infections was characterized by the predominance of Enterobacteriaceae and marked resistance of a number of strains to standard first-line treatment regimens. These findings support the need for regular local microbiological monitoring, revision of empirical antibacterial therapy protocols, and mandatory de-escalation of treatment after culture results become available.