Green Biosynthesis of Gold Nanoparticles Using Lactobacillus Species: Characterization and Antifungal Efficacy Evaluation

Abstract

In recent years, the biological route for producing metallic nanoparticles has attracted considerable attention, mainly because it is eco-friendly and relatively low in cost when compared to the traditional physical and chemical approaches. The present study reports the green biosynthesis of gold nanoparticles (AuNPs) using the cell-free supernatant of a Lactobacillus species, and then evaluates their antifungal activity against selected pathogenic fungi. The bacterial isolate was cultivated in MRS broth, and its supernatant was obtained by centrifugation and mixed with 1 mM chloroauric acid (HAuCl4) under mild conditions. A gradual shift in color from pale yellow to ruby-red was noticed after a few hours, giving the first visual indication of nanoparticle formation. The biosynthesized AuNPs were characterized by UV-Vis spectroscopy, Fourier-transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), and field emission scanning electron microscopy (FESEM). UV-Vis showed a typical surface plasmon resonance band near 535 nm, FTIR indicated the involvement of proteins and other biomolecules as capping/reducing agents, while XRD confirmed the face-centered cubic structure of metallic gold. FESEM images revealed nearly spherical particles with an average size ranging between 20 and 45 nm. The antifungal evaluation, carried out against Candida albicans, Aspergillus niger, and Aspergillus flavus by the agar well diffusion method, showed considerable inhibition zones, with minimum inhibitory concentration (MIC) values between 32 and 128 μg/mL. These findings suggest that Lactobacillus-mediated AuNPs can be regarded as a promising antifungal agent with potential biomedical applications.

Highlights

• AuNPs were successfully synthesized using a cell-free supernatant of Lactobacillus sp.


• The process was simple, rapid, and carried out without any toxic chemicals.


• FTIR, XRD, and FESEM confirmed the formation of crystalline, nearly spherical AuNPs.


• The nanoparticles displayed clear antifungal activity against Candida and Aspergillus species.


• MIC values ranged between 32 and 128 μg/mL depending on the tested fungal strain.