VOLUME 10 NUMBER 2 (July to December 2017)

by Eloise I. Prieto^* and Analiza A. Kiat

National Institute of Molecular Biology and Biotechnology, National Science Complex,    College of Science, University of the Philippines Diliman, Quezon City, 1101 Philippines

The antimicrobial nature of silver nanoparticles (AgNPs) has been exploited commercially due to its broad spectrum activity. Although AgNPs are currently incorporated into numerous medical and consumer products, their action against microbes is not yet fully elucidated. This study investigated the antibacterial activity and mechanism of AgNP on Gram-negative E. coli through analysis of the growth characteristics, permeability, and morphology of AgNP-treated cells. The minimum inhibitory concentration and half-inhibitory concentration of the AgNPs were found to be 55.56 µg ml^-1 and 21.23 µg ml^-1, respectively. Treatment of E. coli with AgNP altered membrane potential and compromised membrane integrity. Time course analysis of treated cells through atomic force microscopy (AFM) revealed nanometer-scale details of E. coli response to AgNP. Images showed that disruption of the outer membrane structure is an early event that precedes damage and disintegration of both E. coli membranes and leakage of its cytoplasmic content. Morphological analysis revealed that hallmarks of cell damage and AgNP toxicity include increase in cell surface roughness and decrease in both cell height and length. The study was able to provide a clearer picture on the membrane-based toxicity mechanism of AgNP by revealing details of AgNP-mediated membrane damage on E. coli cells