Catalase and Oxidase

1
Catalase and Oxidase

• Lab 25

2
CATALASE TEST

• Some bacteria and macrophages can reduce diatomic
  oxygen to hydrogen peroxide or superoxide. Both
  of these molecules are toxic to bacteria.
• Some bacteria, however, possess a defense
  mechanism which can minimize the harm done by the
  two compounds. These resistant bacteria use two
  enzymes to catalyze the conversion of hydrogen
  peroxide and superoxide back into diatomic oxygen
  and water.
• One of these enzymes is catalase.
• The presence of catalase can be detected by a
  simple test.
• The catalase test involves adding hydrogen
  peroxide to a culture sample or agar slant. If
  the bacteria in question produce catalase, they
  will convert the hydrogen peroxide and oxygen gas
  will be evolved.
• The evolution of gas causes bubbles to form and
  is indicative of a positive test.

3
Catalase

• Catalase test is used to test the ability of
  bacteria to degrade hydrogen peroxide by using
  the enzyme catalase.
• The production of bubbles after addition of
  hydrogen peroxide (H202) shows that the catalase
  is present

• 2 H202 -----------------? H20 02

catalase
4
Oxidase

• Cytochrome oxidase is an enzyme found in some
  bacteria that transfers electrons to oxygen, the
  final electron acceptor in some electron
  transport chains. Thus, the enzyme oxidizes
  reduced cytochrome c to make this transfer of
  energy.
• Presence of cytochrome oxidase can be detected
  through the use of Chromogenic reducing agent
  which produces color when oxidized.
• No cytochrome oxidase---No color change indicates
  a negative test.
• Cytochrome oxidase present ---purple color
  indicates a positive test

5
Oxidase

• Oxidase test is used to determine the ability of
  certain bacterial species to produce cytochrome
  oxidase.
• If the cytochrome oxidase is produced, the
  colonies will turn into blue or black coloration
  10-15 seconds after the addition of chromogenic
  reducing reagent