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The organism on the right produced no color, so it does not appear to be a lactose fermenter. MacConkey agar is a selective and differential culture medium for bacteria. It is designed to selectively isolate gram-negative and enteric (normally found in the intestinal tract) bacteria and differentiate them based on lactose fermentation. [1]
Lauryl tryptose broth is used for the most probable number test of coliforms in waters, effluent or sewage. It acts as a confirmation test for lactose fermentation with gas production. Sodium lauryl sulfate inhibits organisms other than coliforms. Formula in grams/litre (g/L) Tryptose: 20.0, Lactose : 5.0, Sodium chloride : 5.0,
Shigella sonnei can ferment lactose, but only after prolonged incubation, so it is referred to as a late-lactose fermenter. During fermentation of the sugar, acid is formed and the pH of the medium drops, changing the color of the pH indicator. Different formulations use different indicators; neutral red is often used. For example, lactose ...
Hektoen enteric agar (HEK, HE or HEA) is a selective and differential agar [1] primarily used to recover Salmonella and Shigella from patient specimens. HEA contains indicators of lactose fermentation and hydrogen sulfide production; as well as inhibitors to prevent the growth of Gram-positive bacteria.
The TSI slant is a test tube that contains agar, a pH-sensitive dye , 1% lactose, 1% sucrose, 0.1% glucose, [2] and sodium thiosulfate and ferrous sulfate or ferrous ammonium sulfate. All of these ingredients are mixed together, heated to sterility, and allowed to solidify in the test tube at a slanted angle.
Endo agar contains peptone, lactose, dipotassium phosphate, agar, sodium sulfite, basic fuchsin and was originally developed for the isolation of Salmonella typhi, but is now commonly used in water analysis. As in MacConkey agar, coliform organisms ferment the lactose, and the colonies become red.
Cystine tryptic agar (CTA), also known as cystine trypticase agar, [1] [2] is a growth medium used for the identification of microorganisms. [3]It can be used to determine if organisms can ferment various carbohydrates, including maltose, lactose, and sucrose.
Rapid lactose fermentation produces acids, which lower the pH. This encourages dye absorption by the colonies, which are now colored purple-black. Lactose non-fermenters may increase the pH by deamination of proteins. This ensures that the dye is not absorbed. The colonies will be colorless. Metallic green sheen of E. coli on EMB agar