Assessment of Antimicrobial Resistance and Virulence of Biofilm-Forming Uropathogenic Escherichia coli from Rio de Janeiro.

Background/Objectives: Uropathogenic Escherichia coli (UPEC) is the leading cause of urinary tract infections in both community and hospital settings worldwide. Antimicrobial-resistant UPEC strains pose a significant challenge for effective antibiotic therapy. In this study, 50 bacterial isolates recovered from urine samples of patients attended in different sectors of a public hospital in Rio de Janeiro over five months were analyzed to assess antimicrobial resistance and virulence profiles through broad gene screening. Methods: Biofilm production was assessed using a semi-quantitative adherence assay. PCR was employed to investigate 27 resistance genes, 6 virulence genes, sequence types (STs), and phylogroups. Susceptibility to 25 antimicrobial agents was determined by disk diffusion testing. Furthermore, the pathogenic potential was evaluated in vivo using the Tenebrio molitor larvae infection model. Results: Most UPEC isolates were moderate or strong biofilm producers (41/50; 82%). The sul1 and sul2 resistance genes were the most frequently detected (58%). Two virulence gene patterns were identified: fyuA, iutA, fimH, cnf1 and fyuA, iutA, fimH (13 isolates; 26%). ST131 and ST73 were the most common sequence types (16% each), and phylogroup B2 was the most prevalent (50%). Thirty isolates (60%) were multidrug-resistant, most of which belonged to phylogroup B2. UPEC exhibited dose-dependent lethality, causing 100% mortality at 2.6 × 10⁸ CFU/mL within 24 h. Conclusions: These findings reinforce the urgent need for surveillance strategies and effective antimicrobial stewardship in clinical practice.