Kessler's nutrient medium is used to identify the Escherichia coli in the sample. This is achieved through the two factors of the nutrient medium. The presence of bile inhibits related nonpathogenic microflora, crystal violet inhibits gram-positive bacteria, and lactose as the sole source of carbon inhibits bacteria that cannot ferment lactose. Applying the glass "float" allows to visually detect the presence of coliforms on the basis of the evolution of gas.