Genomic and Phenotypic Insights into Multidrug-Resistant <i>Escherichia coli</i> ST131 from Urinary Tract Infections: A Clinical and Molecular Investigation

The emergence of Escherichia coli sequence type (ST131), especially its H30Rx subclade, has reshaped the epidemiology of urinary tract infections (UTIs) by combining multidrug resistance (MDR), extended-spectrum β-lactamase (ESBL) production, and biofilm formation. Clinical E. coli isolates were genotyped for ST131 and H30Rx using PCR. Antimicrobial susceptibility, ESBL activity, biofilm formation, and plasmid carriage were assessed through standard protocols. Statistical tests were applied to explore associations between clonal types and resistance traits. Nearly half of the isolates (46.3%) were identified as ST131, with 78.9% belonging to H30Rx. Overall, eight isolates (19.5%) were ESBL producers. ESBL production was significantly higher in ST131 (36.8%) compared with non-ST131 (4.5%; p = 0.004). Plasmid carriage was universal in ST131 (100%) and more frequent than in non-ST131 (86.4%; p = 0.029). MDR was observed in almost 90% of ST131 isolates. Biofilm formation was widespread (97.5%), with all ST131 strains positive. Resistance was greatest against fluoroquinolones and third-generation cephalosporins, while fosfomycin, nitrofurantoin, and amikacin retained high activity with low resistance rates. The predominance of ST131, particularly H30Rx, highlights its role as a high-risk clone driving ESBL production, plasmid-mediated resistance, and biofilm-associated persistence in UTIs. Given the rising resistance to commonly used antibiotics, fosfomycin, nitrofurantoin, and amikacin remain promising therapeutic options. Key limitations include a modest sample size ( n = 41 E. coli isolates), the absence of genotypic ESBL characterization, and the use of disk diffusion for fosfomycin and nitrofurantoin without MIC confirmation. Continuous surveillance, molecular characterization, and strengthened antimicrobial stewardship are essential to control the spread of this lineage and preserve treatment efficacy.