bacterial culture reagents / agar gel / MacConkey agar / for coliforms
for bacterial cultures
agar gels, MacConkey agar
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.