This experiment shows the isolation of Escherichia coli and subsequent growth of the bacterium in pure culture. Both to protect those in contact with the bacterium from infection and to prevent contamination by unwanted microorganisms, great care must be taken to use sterile equipment and materials, employ strictly aseptic techniques, and sterilize all materials contaminated with microorganisms before disposal. MacConkey’s agar and the streak plate method are used to develop a pure colony of E. coli. Experiments demonstrate methods of estimating population size. Inocula from a pure liquid culture of E. coli are introduced into three fermenter growth vessels, each containing a different carbon and energy source. Samples are removed periodically from each vessel to determine population size; the results can be used to explain the control mechanisms operating inside the bacterium. (15 minutes)