biochemical tests

• purpose: tests the ability of an organism to produce the exoenzyme urease, that hydrolyzes urea
• ammonium is alkaline byproduct of urea hydrolysis
• indicatorurea hydrolysis


  phenol red
• + result urea hydrolysis


  Fuschia pink indicates alkaline production
• -result urea hydrolysis


  no color change, orange, or yellow
• urea is a main component of mammalian urine (important urinary tract pathogens)
• SIM REACTIONS (SULFIDE, INDOLE, AND MOTILITY)
• HYDROGEN SULFIDE purpose


  can the bacteria metabolize the amino acid cysteine to produce hydrogen sulfide gas?
• H2S will react with the iron sulfate in the media to produce a black precipitate
• +resulth2s


  presence of black precipitate
• -resulth2s


  no black precipitate present
• Indole purpose


  can the bacteria metabolize the amino acid tryptophan using the enzyme tryptophanase producing indole?
• +result indole


  red ring at top of media
• -result indole


  absence of red ring at top
• motility purpose


  is the bacteria motile?
• +result motility


  turbidity in all directions
• -result motility


  clear stab line
• indole


  kovac's reagent layer becomes red if indole was produced
• MR-VP REACTIONS


  each test species is inoculated into the broth containing glucose (fermentable sugar), peptone (protein source), and a buffer to prevent rapid pH changes
• Methyl red purpose


  can the bacteria produce mixed acids as a result of fermentation, and substantially lower the pH of the medium?
• methyl red pH indicator


  methyl red
• +result methyl red


  pink-red media
• -result methyl red


  yellow media
• Voges-Proskauer purpose


  can the bacteria ferment carbohydrates to produce unusual alcohols, such as acetyl methyl carbinol?
• +result VR


  red ring at suface
• -result VR


  lack of red ring or copper ring
• Ammonium phosphate purpose


  can the bacteria metabolize ammonium as a nitrogen source?
• media in ammonium phosphate test contains ammonium phosphate as a sole nitrogen source
• metabolism of ammonium phosphate produces phosphoric acid
• pH indicator Ammonium phosphate test

  brom cresol purple
• +result ammonium phos. test


  yellow media
• -result ammonium phos. test

  purple media
• Sodium Citrate test purpose

  can the bacteria use citrate using citratase as a carbon source?
• Media in Sodium Citrate test contains citrate as sole carbon source, and an ammonium compound as a nitrogen source
• (sodium citrate) microbes that use citrate will convert the ammonium compound into ammonium hydroxide (alkaline product)
• pH indicator (sodium citrate)


  bromothymol blue
• +result sodium citrate


  royal blue media
• -result sodium citrate 


  green media
• litmus milk purpose


  determine if bacteria produce the exoenzyme caseinase, which hydrolyzes the milk protein casein
• what is also considered in the litmus milk test


  reduction of litmus and lactose fermentation is also considered