Evaluation of Virulence Profiles and Molecular Typing of ESBL-Producing Uropathogenic Escherichia coli: Dominance of ST131 and Emergence of ST421 in Iran.

PURPOSE: Globally, the clonal lineages ST69, ST73, ST95, ST127, and ST131 account for more than half of Uropathogenic Escherichia coli (UPEC) infections. Given the global dissemination and clinical importance of ST131 as a high-risk multidrug-resistant clone, the present study aimed to characterize and compare antimicrobial susceptibility profiles, virulence genes, and resistance determinants of ST131 and non-ST131 UPEC isolates collected from hospitalized patients in Iran over three years (2021-2024). PATIENTS AND METHODS: In this cross-sectional study, 179 confirmed UPEC isolates were examined. Antimicrobial susceptibility testing was performed using the Kirby-Bauer disk diffusion method according to CLSI guidelines, and ESBL production was phenotypically confirmed using the combined disk test (CDT). PCR was performed to detect the bla CTX-M-15 and bla CTX-M-14 genes as well as virulence factors. Common STs were identified via multiplex PCR and MLST, and a clonal relationship was drawn. RESULTS: Overall, 75.4% of the isolates were MDR and 52.5% were ESBL producers, predominantly harboring bla CTX-M-15 (52.5%). The most frequent virulence genes were sat (44.7%), kpsM II-K2 (41.3%), and iroN (40.2%). ST131 was the dominant lineage (63.1%), followed by ST69 (8.4%), ST95 (7.3%), and ST73 (3.9%); notably, ST421 was detected for the first time in Iran. ST131 isolates presented significantly greater resistance to cephalosporins and a stronger association with ESBL production and bla CTX-M-15. Virulence profiles varied across STs, with iroN enriched in ST131. CONCLUSION: This study highlights the dominance of ST131 and the first detection of ST421 among UPEC strains in Iran, with bla CTX-M-15 as the principal ESBL determinant. The heterogeneous virulence landscape underscores the clinical threat posed by MDR clones, emphasizing the need for molecular surveillance and strengthened infection control strategies in hospital settings.