Coliform Bacteria Lab Report

Foodborne illness is probably the most common public health problem in the United States and around the world. It is estimated that millions and millions of Americans gets sick by consuming contaminated food or water each year. Hence it is important to detect the presence of disease-causing bacteria in drinking water. One the simplest way to tell if there is a disease-causing pathogen in the water is the presence of coliform. Just like most of the microorganisms, coliform bacteria, a Gram-negative bacteria that belongs to the bacterial group Enterobacteriaceae, can be found mostly in soil, surface and water. In addition, coliform can be found in the digestive tract, especially in the intestines of animals and humans. While coliform bacteria …show more content…
If there is coliform in the water sample, the color will change from purple to yellow, indicating that the coliform bacteria ferments lactose. The next test that is used to analyze is the EMB agar test, a differential and selective media designed to distinguish the colonies of different microbes and encourage the growth of the desired microbes, while inhibiting the growth of unwanted microbes. Due the media’s composition, it can distinguish microbes that ferment lactose from those that don’t based on the color of the precipitate. For microbes with pink colonies, it means they fermented sucrose, while those that ferment lactose will appear black. As for the non-lactose fermenters, their colonies will appear colorless. The viable count using TSA is a method used to determine the colony forming unit (CFU) based on the cells that are able to grow on the media agar. The variables that are used for this counting method are the number of microbes per plate, the dilution factor, and the volume of liquid inoculated on the plates. The next method is the PetriFilm E.coli/Coliform, where microbes with the enzyme glucuronidase will form red colonies, while E.coli strains will produce blue precipitate due to the presence of beta-glucuronidase. Finally, the MPN procedure relies on multiple dilutions and replicates, because the calculation is based on the dilution factor, volume