Nutrient-TTC Agar (NUT-TTC)
General purpose relatively non-selective agar medium, containing two peptones, which will support the growth of a wide variety of organisms. Suitable for cultivation of both of aerobes and anaerobes. This medium contains the dye, 2, 3, 5- triphenyltetrazolium chloride (TTC) . Aerobic coliform bacteria species grow on this medium and can be detected by their ability to reduce TTC to a red colored formazan dye. Bacterial colonies appear as red dots on an otherwise clear yellowish medium. Agar is the solidifying agent.
MacConkey Agar (MAC)
Both selective and differential; used to differentiate between Gram negative bacteria while inhibiting the growth of most Gram positive bacteria. The medium also differentiates between lactose-fermenting coliforms Lac (+) and lactose non-fermenters Lac (-), which include potential pathogens. Addition to the nutrient agar base of bile salts and crystal violet will inhibit the growth of most Gram-positive bacteria, making MacConkey agar selective. Lactose, a fermentable carbohydrate, and neutral red, a pH indicator, are added to differentiate the lactose positive coliforms from the potentially pathogenic lactose non-fermenters. When lactose is fermented, acid products lower the pH below 6.8, with the resulting colonial growth turning pinkish-red. If an organism is unable to ferment lactose, the colonies will be colorless. Bile salts mixture and crystal violet are the selective agents, inhibiting Gram positive cocci and allowing Gram-negative organisms to grow. Sodium chloride maintains the osmotic environment. Agar and a proprietary polymer are the solidifying agents.
Application
In total coliform testing (TCC), the coliform organisms tested for include: total coliform, fecal coliform, and E. coli (Escherichia coli). Detection of fecal coliforms (a subset of total coliforms) or Escherichia coli (a subset of fecal coliforms) can indicate the potential presence of waterborne pathogens associated with fecal contamination.
