For microbiological time-kill studies, the suspension of bacteria is mixed with the antibiotic at each test concentration. At each time point, the cells are pelleted, resuspended in medium without the antibiotic, and plated on agar, at various dilutions to be sure of having a countable number of colonies. After incubation overnight, the number of colonies is counted to determine the number of viable colonies remaining. A plot is made of the number of colony forming units (CFU) on a logarithmic y-axis versus time on the x-axis.