Green synthesis of silver nanoparticles and testing its effectiveness in inhibiting e. coli, Staphylococcus aureus isolated from urinary tract infections of pregnant women

Abstract

Background: Urinary tract infections (UTIs) are common among pregnant women and are increasingly complicated by antibiotic resistance among causative bacteria, creating a need for alternative antimicrobial strategies such as green-synthesized nanomaterials.

Objective: To green-synthesize silver nanoparticles (AgNPs) using strawberry (Fragaria ananassa) leaf extract and evaluate their antibacterial efficacy against Escherichia coli and Staphylococcus aureus isolated from pregnant women with UTIs.

Methods: Thirty urine samples were collected from Salah El-Din General Hospital (May–July 2022), and bacterial isolates were identified using microscopic examination, biochemical testing, and the Vitek 2 Compact system. AgNPs were synthesized by combining strawberry leaf extract with 1 mM aqueous silver nitrate at room temperature over eight hours, without heating or chemical catalysts. Nanoparticle formation was monitored by color change and characterized using UV-visible spectrophotometry, Fourier-transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM) with energy-dispersive X-ray (EDX) analysis, and X-ray diffraction (XRD). Antibacterial activity was assessed via the agar well diffusion method at AgNP concentrations of 2.5%, 5%, 7.5%, and 10%.

Results: E. coli and S. aureus isolates each accounted for 50% of identified bacteria. A visible color shift from yellow to dark brown confirmed AgNP synthesis, with peak UV-Vis absorbance at 378 nm. SEM revealed spherical to hexagonal, polyaggregated nanoparticles averaging 37.35 nm, with EDX confirming silver (59.54%) and oxygen (40.46%) content. XRD indicated a cubic AgNP crystal structure alongside monoclinic Ag₃O₄ oxide phases. Inhibition zone diameters increased with concentration, reaching 35 mm (E. coli) and 37 mm (S. aureus) at 10% concentration, with no colony growth observed on Mueller-Hinton agar at higher concentrations.

Conclusion: Strawberry leaf extract enabled a low-cost, eco-friendly, catalyst-free green synthesis of AgNPs with concentration-dependent antibacterial activity against UTI-associated E. coli and S. aureus, supporting their potential as an alternative antimicrobial strategy against drug-resistant pathogens.