Aras Part Medical International Press International Journal of Medical Parasitology and Epidemiology Sciences 2766-6492 7 Suppl 1 2026 09 18 Extracellular Biosynthesis and Characterization of Silver Nanoparticles from Clinical Serratia marcescens Isolates Recovered from Urinary Tract Infections and Their Selective Antibacterial Activity Against Gram-Positive Bacteria S48 S56 10.34172/ijmpes.6290 EN Rana H. Raheema https://orcid.org/0000-0002-1360-1716 Ban Hamid Qadoori Dhilal Dhiaa Nasser Roaa M. H. Shoker https://orcid.org/0000-0002-2054-7463 Journal Article 10.34172/ijmpes.6290 2026 03 22 2026 07 11 Introduction: Green microbial synthesis of silver nanoparticles (AgNPs) is an attractive alternative to chemical methods because it is simple, cost-effective, and more environmentally friendly. However, clinically derived bacterial isolates remain insufficiently explored as biofactories for AgNP production and antibacterial testing. This study aimed to biosynthesize and characterize AgNPs using clinical Serratia marcescens isolates recovered from urinary tract infection patients and to evaluate their antibacterial activity against selected Gram-positive and Gram-negative bacteria. Methods: One hundred urine samples were collected from intensive care unit patients. Serratia marcescens isolates were identified by conventional methods. Antibiotic susceptibility was assessed. AgNPs were synthesized extracellularly from bacterial supernatant and characterized by UV-Vis spectroscopy, EDX, FE-SEM, and AFM. Antibacterial activity was tested by agar well diffusion using AgNP concentrations of 125, 62.5, 31.25, 15.6, 7.8, and 3.9 µg/ml. Results: Sixteen of 100 urine samples (16%) yielded S. marcescens. The isolates showed high resistance to co-amoxiclav (100%), cefotaxime (62.5%), and ceftriaxone (56%), while the highest sensitivity rates were observed for amikacin (100%), gentamicin (94%), and ciprofloxacin (81%). Biosynthesized AgNPs showed a surface plasmon resonance peak at 445 nm. EDX confirmed silver with an atomic weight percentage of 17.9%. FE-SEM showed predominantly spherical particles with an estimated size range of 50-100 nm, whereas AFM indicated nanoscale surface features ranging from 0.0 to 14.1 nm. In antibacterial testing, the strongest inhibition was recorded against Staphylococcus aureus at 125 µg/ml (28.33 ± 0.33 mm), followed by S. lugdunensis, S. haemolyticus, and S. epidermidis. Conclusion: Clinical S. marcescens isolates were able to extracellularly synthesize AgNPs with confirmed nanoscale characteristics. The biosynthesized AgNPs showed selective antibacterial activity against Gram-positive bacteria. These findings support the biomedical relevance of clinically derived bacterial systems for green nanoparticle production while also highlighting the need for broader characterization and expanded biological validation.