Biofilm Formation, Virulence-Associated Genes, and Antimicrobial Resistance in Proteus mirabilis Isolates from Urinary Tract Infections in Iran.

Proteus mirabilis is a frequent cause of complicated urinary tract infections (UTIs), in which biofilm formation and antimicrobial resistance contribute to persistence and therapeutic failure. This study investigated the biofilm-forming capacity, antimicrobial resistance profiles, virulence-associated genes, and genetic diversity of P. mirabilis isolates recovered from UTI patients in Isfahan, Iran. A total of 104 non-duplicate clinical isolates were analyzed. Biofilm formation was quantified using a microtiter plate crystal violet assay, and antimicrobial susceptibility testing was performed according to CLSI guidelines. Extended-spectrum β-lactamase (ESBL) production and extended-spectrum cephalosporin resistance (ESCR) were assessed phenotypically and by PCR. Selected virulence- and biofilm-associated genes were detected by PCR, and clonal relatedness was evaluated using ERIC-PCR. Most isolates were capable of biofilm formation, with 51% classified as strong and 45.2% as moderate producers. High carriage rates of virulence- and biofilm-associated genes, including zapA, zapD, ureC, ureR, luxS, rsbA, and acrA, were observed. ESBL production and ESCR phenotypes were detected in 6.7% and 12.5% of isolates, respectively, while multidrug resistance was observed in 30.4% of isolates. ERIC-PCR analysis identified predominant clonal clusters among isolates exhibiting strong biofilm production. These findings highlight the coexistence of biofilm formation, virulence determinants, antimicrobial resistance, and clonal diversity in uropathogenic P. mirabilis in this region.