Enterobacteriaceae

Purpose: TSI agar can be considered an initial step in the identification of the [blank_start]Enterobacteriaceae[blank_end]

Principle: for [blank_start]Indole Broth[blank_end]: tryptophan PRESENT in peptone is oxidized y certain bacteria to indole, skatole, and indoleacetic acid. Indole is detected in broth cultures of bacteria with an alcoholic p-dimethylaminobenzldehyde reagent. Indole reacts with the aldehyde to form a [blank_start]red[blank_end] product.

Key Ingredients: [blank_start]Indole broth[blank_end]: Tryptophan (1% broth), Kovac's reagent or Ehrlich's reagent, Xylene or chloroform for extraction if using Ehrlich's reagent

Indole Broth Reactions: Negative Reaction: [blank_start]No[blank_end] color development Positive Reaction: [blank_start]red[blank_end] ring at the interfacec of reagent and broth) Variable reaction: [blank_start]Orange[blank_end] color, indicates production of aktole, a methylated intermediate that may be a precursor to indole production

Principle: Urea Hydrolysis (Christensen's Agar): Many organisms possess the enzyme urease which can hydrolyze urea with the release of ammonia and carbon dioxide which acts to increase the pH of the medium and turn the indicator phenol red from pale [blank_start]orange[blank_end] to dark [blank_start]fuchsia pink[blank_end]

Key Ingredients: Urea Agar Urea Agar ([blank_start]christensen's Base[blank_end]) pH indicator = [blank_start]phenol red[blank_end]

Interpretation: urea hydrolysis A strong positive hydrolysis test: entire agar, slant and butt, turning [blank_start]deep pink[blank_end] after overnight incubation. A moderate positive test: [blank_start]pink[blank_end] slant at 24 hours, with the intensity of the color increasing with extended incubation A negative test: no change from pale [blank_start]orange[blank_end] color of the slant