OXIDASE TEST

Effective Date: 
Thu, 08/01/2013
Reviewed: 
Tue, 01/10/2017
Revised: 
Thu, 08/01/2013
Policy: 

 

Purpose and Scope:

Cytochrome containing organisms produce an intracellular oxidase enzyme. This oxidase enzyme catalyzes the oxidation of cytochrome c. Organisms which contain cytochrome c as part of their respiratory chain are oxidase-positive and turn the reagent blue/purple. Organisms lacking cytochrome c as part of their respiratory chain do not oxidize the reagent, leaving it colorless within the limits of the test, and are oxidase-negative.

OxiStrips™ Oxidase Strips are ready to use test strips with a convenient plastic handle so the user can avoid skin contact with the reaction area.

OxiSticks™ Oxidase Swabs are swabs containing reagents impregnated in the tip of the swab for ease of use.

 

 

Reagents and Supplies:

  • Hardy Oxistrips test kit
  • Sterile H2O
  • Sterile inoculating loop or stick

 

Reagent Storage

  • Upon receipt store at 15-30 degrees C.
  •  Products should not be used if there are any signs of deterioration or if the expiration date has passed.
  •  Store OxiStrips™ and OxiSticks™ with a desiccant in the vial at all times.
  • The expiration date applies to the product in its intact packaging when stored as directed.

 

Quality Control:

 

QC is performed on each day the test is performed. Use procedure with stock culture of P aeruginosa ATCC 27853   (Oxidase positive) and E. coli (ATCC 25922) (Oxidase negative).

Record QC results on Oxidase Test QC Log.

 

Procedure

  1. Place oxidase test strip in a petri dish and moisten an area of the strip to be tested with water. Do not saturate strip.
  2. With a sterile inoculating loop or wooden applicator stick, smear a bacterial paste from 3-4 well isolated colonies onto the moistened area. Use colonies that are 18-24 hours old.
  3. Appearance of a blue/purple color within 30 seconds indicates a positive test.
  4. Important: Any color appearing after this time should be disregarded.

 

Limitations

 

The oxidase test may be used in the presumptive identification of Neisseria spp. and in the differentiation and identification of gram-negative bacilli. All oxidase-positive organisms should be examined by gram stain to determine cellular morphology and gram reaction. Additional biochemical testing, using pure culture, is recommended for complete identification.

Using nichrome or other iron containing inoculating devices may cause false-positive reactions.

Oxidase reactions of gram-negative bacilli should be determined on colonies obtained from non-selective and non-differential media to ensure valid results.

Most Haemophilus spp. are oxidase-positive. Less sensitive oxidase test strips or reagents may yield false-negative results.

Weakly oxidase-positive organisms, such as Pasteurella multocida, may take longer to show a positive reaction on the test strips.

It is recommended to use colonies that are 18-24 hours old. Older colonies may produce weaker reactions.

The oxidase test should be performed on isolates at or above 15-30 degrees C.

Any color development appearing after 30 seconds of inoculation should be disregarded.

 

 

 

 

REFERENCES

 

Hardy Oxistrips Test Kits Package Insert Copyright 2002

MacFaddin, J.F. 1980. Biochemical Tests for the Identification of Medical Bacteria, 2nd ed. Williams & Wilkins, Baltimore, MD.