Oxidase test

Background

• Identifies cytochrome C oxidase by testing for the ability to oxidize tetramethyl-p-phenylenediamine to indophenols, which are purple
• The test is positive when it turns purple within 10 seconds
  • Must be done from plain 5% SBA

Interpretation

• All oxidase-positive bacteria are aerobic
  • P: Pseudomonas
  • V: Vibrio cholerae
  • N: Neisseria
  • C: Campylobacter
  • H: Helicobacter and Haemophilus
  • Aeromonas

Oxidase-Positive Organisms

	Stain	Shape	Oxidase
Achromobacter	Gram-negative	bacillus	positive
Aeromonas	Gram-negative	bacillus	positive
Alcaligenes faecalis	Gram-negative	bacillus	positive
Brucella melitensis	Gram-negative	coccobacillus	positive
Burkholderia pseudomallei	Gram-negative	bacillus	positive
Campylobacter	Gram-negative	bacillus	positive
Francisella tularensis	Gram-negative	coccobacillus	positive negative
Helicobacter pylori	Gram-negative	bacillus	positive
Herbaspirillum	Gram-negative	bacillus	positive
Micrococcus	Gram-positive	coccus	positive
Moraxella catarrhalis	Gram-negative	diplococcus	positive
Neisseria	Gram-negative	diplococcus	positive
Ochrobactrum anthropi	Gram-negative	bacillus	positive
Pasteurella	Gram-negative	bacillus	positive
Pseudomonas aeruginosa	Gram-negative	bacillus	positive
Vibrio	Gram-negative	bacillus	positive
Vibrio cholerae	Gram-negative	bacillus	positive
Vibrionaceae	Gram-negative	bacillus	positive

Oxidase-Negative Organisms

	Stain	Shape	Oxidase
Acinetobacter ursingii	Gram-negative	coccobacillus	negative
Cronobacter sakazakii	Gram-negative	bacillus	negative
Erysipelothrix rhusiopathiae	Gram-positive	bacillus	negative
Francisella tularensis	Gram-negative	coccobacillus	positive negative
Listeria monocytogenes	Gram-variable Gram-positive	bacillus pleomorphic	negative
Proteus	Gram-negative	bacillus	negative
Raoultella	Gram-negative	bacillus	negative
Raoultella ornithinolytica	Gram-negative	bacillus	negative
Stenotrophomonas maltophilia	Gram-negative	bacillus	negative

Further Reading

• Microbe Online. Oxidase Test: Principle, Procedure and Oxidase-Positive Organisms.