Avaliação da atividade antimicrobiana de nanopartículas de prata biossintetizadas pelo fungo Aspergillus niger

Abstract

The following work proposes synthesis of silver nanoparticles through biological methods, mediated through Aspergillus niger fungi, an organism widely known for its spontaneous metal reduction capacity. The biosynthesis can be segmented in two major processes, obtention of the fungal cells and silver nitrate reduction. The first process consisted of cultivating the fungus on its optimal conditions, separating the spores originated from the solid culture and growing the fungus in liquid media, resulting in the cell filtrate. The cell filtrate was then used for the second step of this process, adding a silver nitrate solution to the cell filtrate, promoting the nitrate’s reduction, originating the silver nanoparticles, observed through a change in the solution’s color, from a turbid white to shades of brown. The characterization of the nanoparticles was made through UV-vis spectroscopy and transmission electronic microscopy, methods that allow further analysis of the nanoparticles’ shape and size. For the verification of the suspension’s anti-bacterial effects, different species of bacteria were submitted to the well plate method, which consists on cultivating the colonies on a Petri plate with wells containing different concentrations of the colloidal suspension, resulting on hollow ring zones around the disks, indicating the anti-microbial activity. In this paper, the obtained results were similar for the AgNP1 and AgNP3 conditions, with silver concentrations equivalent to 571,6263 mgL-1 and 584,3510 mgL-1 respectively, while for AgNP2 a concentration of 406,9420 mgL-1 was obtained. All samples presented bands between 400 and 500 nm on UV-vis spectrophotometry, as expected for silver nanoparticles, with absorbances between 0,4 and 0,5 abs. The biosynthesized nanopartciles’ size is compatible with the literature, ranging from 37,5 to 47,3 nm. For the biological tests, there’s a similar result on the halo’s diameter observed on the well diffusion test, while the MIC presented a better result for Clostridium perfringens on AgNP3 conditions, with a minimal inhibitory concentration of 36,5220 mgL-1. For MBC, the best concentrations were obtained from the dilutions of 12,5% of the suspensions, matching with the MIC results.