Revista de bioanálisis y biomedicina

Antimicrobial Activity of Biosynthesized Silver Nanoparticles against E. coli and B. subtilis

Abstract

Salwa Al-Thawadi*, Alaa Shukralla A. Rasool and Khaled Youssef

Silver nanoparticles (AgNPs) are used increasingly in medical and agricultural sectors for disease management, due to their antimicrobial activity. In the current study, Biosynthesized AgNPs produced from a previous study (AgNPs1, AgNPs2 and AgNPs3) were used to test their toxicity on gram negative (E. coli) and gram positive (B. subtilis) bacteria. These nanoparticles (NPs) were examined by scanning electron microscopy (SEM), energy dispersive X-ray analysis (EDS) and X-ray diffraction (XRD). SEM micrographs show that AgNPs1 were almost spherical monodispersed while AgNPs2 were aggregated. More aggregations appeared in AgNPs3. Peaks of AgNPs are obvious in the EDS which were confirmed further by XRD peaks ascertaining the precipitation of AgNPs. Toxicity effect of AgNPs was tested by exposing E. coli and B. subtilis to AgNPs1, AgNPs2 and AgNPs3 during their growth. Bacterial growth was followed by OD at 600 nm. Unexpectedly, an enhancement effect was proven in the presence of AgNPs1 for both bacterial strains, whereas an inhibition effect of bacterial growth was proven in the presence of AgNPs2 and AgNPs3. AgNPs3 were selected to test their minimum toxicity effect against E. coli and B. subtilis which shown to be 10 mg.L-1. To our knowledge, this study was the first study to show bacterial growth enhancement effect for AgNPs. The reasons for this enhancement need further investigation.