Biochemical Properties

• Filtration is used to sterilize heat-labile substances like serum, plasma, and carbohydrate solutions
• Lyophilization is a process known as freeze-drying
• Ultracentrifugation involves the use of a centrifuge
• Chemical methods of destruction in microbiology include: Disinfection, Bactericidal, BacteriostaticChemical
• Disinfection is the process of removing or killing microorganisms using a chemical agent
• Bactericidal refers to the killing of bacteria
• Bacteriostatic agents inhibit only the growth of bacteria
• Biochemical properties in microbiology:

  • Biochemical tests demonstrate the enzyme system within microbial cells
  • CHO Fermentation Test involves the anaerobic breakdown of substances
• During fermentation, simple sugars serve as the main source of energy for microorganisms
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  • Media used in microbiology include:
  • °TSI (triple sugar iron)
  • KIA (Klingler iron agar)
  • RDA (Russel’s double agar)
• TSI contains glucose (0.1%), lactose (1%), sucrose (1%), and iron
• KIA contains glucose, lactose, and iron
• RDA contains glucose and lactose
• IMViC reaction (Indole Methyl Red Voges-Proskauer Citrate Test) involves media like:

  • Tryptophan broth for the indole test
  • MRVP medium or Clark & Lubs Dextrose Broth medium
  • Simmon Citrate Test
• Indole Test:

  • To observe for a positive result, add ether or xylene to extract indole, then add Ehrlich’s or Kovac’s reagents
  • Positive result: formation of deep red color
  • Principle: some organisms can split tryptophan into alanine and indole, which combines with p￾dimethylaminobenzaldehyde in Ehrlich’s or Kovac’s reagent to produce a deep red color
• Methyl Red Test:

  • After incubating the inoculated MRVP medium, add 5 drops of Methyl Red indicator
  • Positive result: formation of deep red color
  • Principle: Organisms fermenting dextrose produce large amounts of acids, and this test is based on the final hydrogen ion concentration (pH) reached by the culture
• Voges-Proskauer Test:

  • After incubating the inoculated MRVP medium for 48 hours, add:
  • 15 drops of 5% alpha naphthol in ethyl alcohol
  • 10 drops of 0.3% of creatine in 40% KOH
  • Principle: when glucose is fermented, some organisms produce not only acid but also a compound known as acetyl methyl carbinol or acetoin, which in the presence of KOH will be oxidized to dimethyl carbinol, reacting with guanidine compounds in the broth to produce a deep red color
• Simmon Citrate Test:

  • pH indicator: Bromthymol blue
  • Positive result: Prussian blue color
  • Principle: some organisms can utilize citrate as the sole source of carbon, releasing ammonia gas which makes the medium alkaline, turning the pH indicator from green to blue
• Catalase Test:

  • Negative result: because catalase is also present in the RBC
  • Principle: some organisms elaborate the enzyme catalase, liberating hydrogen peroxide to form oxygen
• Oxidase Test:

  • (+) for oxidase test: Pseudomonas sp; Neisseria sp
  • Oxidase reagent: paraaminomthylaniline monohydrochloride or tetramethylparaphenylene diamine dihydrochloride
  • Principle: colonies producing the enzyme endophenol oxidase becomes pink changing to red, then black upon the addition of oxidase reagents. While the colony is in the pink stage, the organisms are still viable; when the colonies turn black, organisms are dead
• Urease Test:

  • Medium: Christensen’s urea agar; pH indicator: phenol red
  • (+) result: dark pink or red color
  • Principle: some organisms can hydrolyze urea rapidly releasing ammonia in the process
• PAD (Phenylalanine Deaminase Test):

  • (+) result: dark green color after addition of ferric chloride
  • Principle: some organisms can deaminate phenylalanine converting it to phenylpyruvic acid
• Lysine Decarboxylase Test:

  • pH indicator: Bromcresol blue
  • Medium: LIA or Moeller’s medium
  • (+) result: medium remains in purple in color
  • (-) result: yellow color