CARBON AND CLAY NANOPARTICLES PROVOKE NUMEROUS REPSONSES IN SALMONELLA ENTERICA VAR. TYPHIMURIUM AND ESCHERICHIA COLI
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Nanoparticles are classified by having at least one dimension of the particle measuring less than 100 nm. Due to their large surface area to volume ratio, nanoparticles may have unusual and unique properties not attributed to larger particles, and are often be more reactive. Nanoparticles have become widely used in many products in the past twenty years, including cosmetics, paints, clothing, electronics, and medical equipment. Because nanoparticles are becoming increasingly common and widespread, it is crucial to recognize not only how these particles can impact human health and the environment, but it is fundamental to understand how nanoparticles affect organisms on a smaller scale, such as bacteria. The studies described here focused on multiple Escherichia coli and Salmonella enterica var. typhimurium strains. Using the Ames test, increasing concentrations of three nanoparticles were examined to detect a mutagenicity effect. Multi-walled carbon nanotubes, halloysite nanotubes, and Cloisite® Na+ nanoparticles were tested and it was found that the nanoparticles did not have a true mutagenic effect, although all three nanoparticles exhibited potential for weak toxicity effects. Further toxicity tests were conducted under light, dark, aerobic, and anaerobic conditions, demonstrating that the nanoparticles resulted in levels of toxicity that varied according to strain. Some nanoparticles appeared to possibly elicit oxidative stress in S. typhimurium, as evidenced by decreased survival of S. typhimurium SGSC 1336 oxyR- when treated with the multi-walled carbon nanotube (P < 0.001). This study concludes that nanoparticles may not have a general toxic effect across all bacterial species; rather species-specific responses are demonstrated.