Escherichia coli is a significant pathogen in extraintestinal infections, and ESBL-producing E. coli poses a major clinical challenge due to its antibiotic resistance. This study comprehensively analyzed E. coli isolates from urine and blood samples of patients with urinary tract and bloodstream infections at three major tertiary hospitals in South Korea. The goal was to provide insights into the distribution, antibiotic resistance, and virulence factors of these strains. Our analysis identified CTX-M and TEM as the dominant ESBL types, found in 71.7% and 61.7% of isolates, respectively, with 46.7% showing co-occurrence. Multilocus sequence typing (MLST) revealed the predominance of high-risk clones such as ST131, ST69, ST73, and ST95, with rare sequence types like ST410 and ST405 also identified. The high prevalence of virulence factors, including iutA (80.8%) and kpsMII (74.2%), further highlights the complexity of these strains. In addition, 38.3% of clinical isolates contained a combination of siderophore, adhesin, protectin, and toxin-related genes. There was no significant difference between urinary tract and bloodstream infections or regional differentiation in Korea. This study highlights the importance of controlling ESBL-producing E. coli infections, especially given the increasing incidence among patients with underlying medical conditions and older adults who are more susceptible to urinary tract infections. These findings serve as valuable indicators for pathogen analysis, especially those harboring antibiotic resistance and toxin genes. The insights gained are expected to contribute significantly to the development of infectious disease prevention and control strategies.

Department of Biomedicine and Health Sciences and Integrated Research Center for Genomic Polymorphism Precision Medicine Research Center College of Medicine The Catholic University of Korea Seoul Republic of Korea

Department of Convergence Medical Science Gyeongsang National University Jinju Republic of Korea

Department of Laboratory Medicine Gyeongsang National University Hospital Jinju Republic of Korea

Department of Microbiology College of Medicine Gyeongsang National University Jinju 52727 Republic of Korea

Department of Sciences and Liberal Arts Mahidol University Amnatcharoen Campus Amnatcharoen Thailand

Fastidious Specialized Pathogen Resources Bank A Member of the National Culture Collection for Pathogens Gyeongsang National University Hospital Jinju Republic of Korea

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