Iranian Journal of Medical Microbiology

Background and Aim: Nanoemulsion technology is recognized as one of the most advanced and targeted drug-delivery systems. The purpose of this study was to determine the effectiveness of a trimethoprim-based nanoemulsion against Proteus mirabilis isolated from urinary tract infections (UTIs).
Materials and Methods: 300 urine samples were collected from patients previously diagnosed with UTIs by specialized physicians at Azadi Teaching Hospital. Urine samples were inoculated onto blood agar and MacConkey agar. Phenotypic identification was conducted; P. mirabilis was confirmed by using the 16S rRNA gene. Antibiotic susceptibility was tested using the Kirby–Bauer method. Trimethoprim nanoemulsions were formulated via phase diagram construction, characterized by FTIR, zeta potential, and FESEM, and evaluated for stability and antimicrobial activity.
Results: The isolation rate of P. mirabilis was 50 (28.57%) isolates from 175 culture-positive samples. Species confirmation was performed by detecting the 16S rRNA gene, a conserved molecular marker, using PCR, which yielded a single 1500 bp band in all isolates. The results revealed that P. mirabilis exhibited complete resistance (100%) to ampicillin, 50% resistance to trimethoprim, nalidixic acid, and ciprofloxacin, and 30% resistance to gentamicin. FTIR analysis confirmed that no major chemical interactions occurred between trimethoprim and the excipients, ensuring drug stability. FESEM imaging demonstrated a uniform spherical morphology of nanoemulsion droplets, which correlates with its stability and bioactivity. The mean inhibition zone diameter for the trimethoprim nanoemulsion against P. mirabilis was 41.5 mm, which was significantly larger than that of pure trimethoprim alone (p < 0.001).
Conclusion: All the isolates showed complete susceptibility to the trimethoprim nanoemulsion, indicating its potent antibacterial activity.