Assays Evaluating Antimicrobial Activity of Nanoparticles: A Myth Buster

The kingdom of interdisciplinary research is advancing forcefully; nanotechnology is one discipline that has impressed biologist, physicist, chemists, engineers and physicians. For studying the antimicrobial activity of nanomaterials, standard protocols that were used earlier for assessing the efficiency of antibiotics and compounds were taken for granted. The disc diffusion and well diffusion methods were ideally designed for studying bactericidal activity of diffusible compounds, mainly antibiotics and not for a particulate interaction based systems. A mere extrapolation of the testing method for testing nanoparticles, with an exclusion of the plate count method, appears to have stepped out of the fundamental principle whereby nanomaterials and microbes are required to interact. This report highlights the flaw in the results obtained from using disc/well diffusion methods for determining the bioactivity of nanomaterials, owing to the physical barrier between bacteria and the nanoparticles. A more realistic and reliable method, where the nanoparticles and microbial cells are put into an open base where they can freely interact is mandatory to assess toxicity/compatibility of nanomaterials. Failure in utilizing the apt testing mode, may eventually lead to declaring toxic nanomaterials as non-toxic and underestimating the antimicrobial ability of few other potent nanomaterials.