Biogenic synthesis of silver nanoparticles by Lactobacillus planetarium isolated from fermented sorghum bicolor and in vitro antimicrobial activities

Abstract

The need for novel antimicrobial agents has driven interest in the synthesis of nanoparticles with broad-spectrum antimicrobial potential.  This study was undertaken to synthesize silver nanoparticles (Ag-NPs) using Lactobacillus plantarum from fermented  sorghum. The Ag-NPs were characterized using UV-vis spectrophotometer, X-ray diffractometer, and IR-470 spectrometer. The  antimicrobial efficacies of Ag-NPs were determined by the agar well diffusion method. The UV-Vis spectroscopy analysis showed that the  Ag-NPs had an absorption peak at 420 nm. Of the sixteen isolates tested, 25 µg/mL of biosynthesized AgNPs inhibited 81.3% of isolates,  100 µg/mL of biosynthesized AgNPs inhibited 93.8% of isolates, while all the isolates were sensitive to biosynthesized AgNPs at a  concentration of 200 µg/mL. The lowest and highest mean zone of inhibition obtained was 9.2 ± 0.2 mm and 20.0 ± 1.0 mm, respectively.  The minimum inhibitory concentration (MIC) ranged from 6.25 μg/mL for S. aureus, C. freundii, P. aeruginosa, C. dubliniensis, and C. parapsilosis to 100 μg/mL for S. flexneri and C. glabrata. The minimum bacteriocidal concentration (MBC) and minimum fungicidal  concentration (MFC) values of biosynthesized AgNPs ranged between 12.5 to ˃200 μg/mL. The MBC/MIC biosynthesized AgNPs on  bacterial isolates and MFC/MIC ratios of biosynthesized AgNPs on Candida isolates ranged from 1 to 4 and 2 to 4, respectively. The  regression values of biosynthesized AgNPs, as exhibited by the bacterial and Candida isolates, ranged from 0.6049 to 0.9285 and 0.5750 to  0.8902, respectively. Biosynthesized AgNPs from the CFS of L. plantarum demonstrated broad-spectrum antimicrobial activity, with  MBC and MFC values confirming their bactericidal and fungicidal effects.