Does the shape of nanoparticles affect the evolution of resistance to silver? In an earlier study we demonstrated that E. coli K12 MG1655 could rapidly evolve resistance to spherical nanoparticles. In ongoing work, we showed that this bacterium easily evolved resistance to ionic silver. To test the effect of nanoparticle shape, we established 5 replicate populations exposed to triangular silver nanoparticles (AgNPl); 5 replicates exposed to spherical silver nanoparticles (AgNP), 5 exposed to ionic silver (Ag+) in the form of AgNO3, and 5 controls for a total of 20 replicates. The AgNPl and AgNP were citrate- coated. In the AgNPl replicates, we observed a minimal response to selection over the first 100 generations (~15 days). Minimum inhibitory concentration (MIC) had increased from 12.5 mg/L to 18 mg/L. In both the AgNP and Ag+ replicates, MIC continued to increase as in our past experiments. The measured MIC in the AgNPl-exposed replicates began to decline after 100 generations. By generation 230 (~35 days) all of the AgNPl lines were extinct. We maintained the selection lines at 100 g/L, a concentration that showed positive selection results for both the spherical AgNP-selection and Ag+-selection replicates. We are in the process of repeating this experiment. We are currently maintaining 10 AgNPl-selected replicates at a culture concentration of 40 g/L. We will test these replicates for 24-hour growth at this concentration to determine if we observe superior growth relative to controls. These preliminary results suggest that nanoparticle shape does impact the evolve ability of silver resistance.
Author: Dr. Marjan Assefi