Oxidase
enzymes play a vital role in the operation of the electron transport system
during aerobic respiration. Cytochrome oxidase catalyses the
oxidation of a reduced cytochrome by molecular oxygen (O2),
resulting in the formation of H2O or H2O2. Aerobic bacteria as well as some
facultative anaerobes and microaerophiles, exhibit oxidase activity. The oxidase test aids in differentiation
among members of the genera Neisseria and
Pseudomonas, which are oxidase
positive, and Enterobacteriaceae, which are oxidase negative.
Aim
To
distinguish among groups of bacteria on the basis of cytochrome oxidase
activity.
Principle
The
ability of bacteria to produce cytochrome oxidase can be determined by the
addition of the test reagent, p-aminodimethylaniline
oxalate, a reagent which serves as an artificial substrate, donating electrons
and thereby becoming oxidized to a blackish compound in the presence of the
oxidase and free oxygen. The dark coloration
is indicative of cytochrome oxidase production and represents a positive
test. No color change is indicative of
the absence of oxidase activity and is a negative test.
Requirements
24 hr
nutrient broth cultures of species Bacillus,
Staphylococcus, Streptococcus, Pseudomonas and E.coli.
Oxidase
strips containing p-aminodimethylaniline
oxalate, Bunsen burner, glass rod, glass marking pencil etc.
- Remove oxidase strips from the container and place in a petridish.
- With the help of a clean glass rod / plastic loop or platinum wire pick a colony from 24 hrs growth of the test organism and rub over the filter paper. Do not use nichrome wire.
- Observe the color change within 5-10 sec.
Pseudomonas sp. produced an
intense deep blue color within 5-10 sec indicating a positive result. Bacillus,
Staphylococcus, Streptococcus and E.coli
produced no change in color.
Pseudomonas
sp. is oxidase positive whereas Bacillus,
Staphylococcus, Streptococcus and E.coli
are oxidase negative.
No comments:
Post a Comment
Note: Only a member of this blog may post a comment.