Biosynthesized silver nanoparticles show antimicrobial properties

Researchers found that increasing the concentrations of the biosynthesised nanoparticles decreased the amount of Salmonella typhimurium.

Tripathi et al studied the biosynthesis of silver nanoparticles (AgNPs) using fungal biomass of Trichoderma koningii and evaluation of antibacterial activity.

Biological synthesis of metal nanoparticles involving the use of plants and micro-organisms is an alternative for physical and chemical methods, said the researchers.

The fungal biomass releases enzymes and proteins which help in production of silver nanoparticles between 8–24 nm.

Trichoderma koningiiis a non-pathogenic and agricultural fungus which antagonises plant pathogens.

Nanoparticles vs bacterial growth​

Biosynthesized silver nanoparticles were characterized by UV–Vis spectroscopy, dynamic light scattering (DLS), transmission electron microscopy (TEM) and x-ray diffraction (XRD).

In the absence of AgNPs, there is an increase of optical density indicating the rise of bacterial growth, but as the AgNPs concentration increases optical density decreases showing reduction of bacterial growth rate.

Optical absorption was insignificant at 45μg ml−1 concentration of AgNPs. This means that at this concentration the bacterial growth does not take place. The minimum inhibitory concentration (MIC) of AgNPs was 25μg ml−1.

The high antibacterial activity of AgNPs was due to its high surface-to-volume ratio.

Study method​

To study the bacterial growth in broth media, fresh colonies on agar media were inoculated in 10ml of broth.

This media was supplemented with biosynthesized AgNPs ranges from 20 to 45μg ml−1 and the bacterial culture was incubated at 37 degrees with continuous shaking at 150 rpm.

Growth of Salmonella typhimurium in broth media was indexed by measuring the optical density (OD) at 600nm at regular intervals using UV–Vis spectroscopy.

The control culture was treated in the same way but without exposure to the silver nanoparticles. The growth curve was plotted between optical density and time.

Biosynthesis of nanoparticles using fungus is advantageous compared to plants because fungus produces more protein which results in high production of nanoparticles and provides longer stability, according to the researchers.

Source: Advances in Natural Sciences: Nanoscience and Nanotechnology

Online ahead of print, doi: 10.1088/2043-6262/4/3/035005​

“Trichoderma koningiiassisted biogenic synthesis of silver nanoparticles and evaluation of their antibacterial activity”​

Authors: R M Tripathi, Rohit Kumar Gupta, Archana Shrivastav, M P Singh, B R Shrivastav, and Priti Singh