4. Analytical methods for antimicrobial activity

To test the antimicrobial effects of nanoparticles, several analytical methods are employed. Bacteria or yeasts are grown in liquid culture media, which provide them with the nutrients they need to grow and multiply. At 37°C in a rich medium, certain bacterial strains, such as E. coli, divide to give a new generation every 20 minutes. Some yeasts, such as S. cerevisiea, divide every 2 hours. In this way, in the absence of nanoparticles, bacteria or yeast divide rapidly. The growth of a microbial population in a non-renewed liquid culture medium can be quantified by measuring optical density over time (figure