Cat. no. Z19 Oxidase Powder, 10mL amber tube, 0.1gm 20 tubes/box
Cat. no. Z119 OxiDrop™, Oxidase Test, 0.5oz. Polyethylene Bottle with Dropper Tip, 7.0ml 1 each


Hardy Diagnostics OxiDrop™, Oxidase Test is a liquid ready-to-use reagent that is used in procedures to detect cytochrome oxidase activity in bacteria. Oxidase Powder can be used to prepare the oxidase reagent.


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.


N,N,N',N'-tetramethyl-p-phenylenediamine Dihydrochloride 12.0gm
Distilled Water 1000.0ml
Stabilizing Agent

* Adjusted and/or supplemented as required to meet performance criteria.


Storage: Upon receipt store Cat. no. Z119 at 2-8ºC and Cat. no. Z19 at 2-30ºC away from direct light. Product should not be used if there are any signs of deterioration, discoloration, contamination, or if the expiration date has passed. Product is light and temperature sensitive; protect from light, excessive heat, moisture, and freezing.



For. Cat. no. Z19: Add 10mL deionizied water to one tube of oxidase powder containing 0.1gm of oxidase powder. Use the prepared oxidase reagent by following the procedure for Cat. no. Z119 below.

For. Cat. no. Z119: Use only 18-24 hour old colonies from non-selective, non-differential media.

Place a piece of filter paper in a sterile, plastic, disposable petri dish. Moisten the piece of filter paper with a few drops of oxidase reagent. Rub a small amount of the colony to be tested onto the paper using a platinum loop or a wooden applicator stick. Observe for blue-black color development.

Alternatively, a drop of the reagent can be placed directly on a colony on an agar plate, looking for the same color development described above.(2)


Development of a blue-black color within 10-20 seconds indicates that the organism is positive for the presence of cytochrome oxidase.

Important: Any color change after 20 seconds should be disregarded.


The oxidase test can be used in the presumptive identification of Neisseria spp. and in the differentiation and identification of gram-negative bacilli. Oxidase-positive organisms should be examined by gram stain to determine morphology and gram reaction. Additional biochemical tests are recommended for complete identification.

Use of a nichrome or other iron containing loop may yield false-positive reactions. Platinum loops are recommended.

Most Haemophilus spp. are oxidase-positive. Less sensitive strips or reagents may yield false-negative results. Consult listed references for more information. (7)

Oxidase reactions of gram-negative bacilli should be determined on non-selective and non-differential media to ensure valid results. Also, colonies taken from media containing high levels of glucose may give false-negative reactions. (5)

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

Any color changes appearing after 20 seconds should be disregarded.


Standard microbiological supplies such as filter paper, empty petri dishes, platinum loops or wooden applicator sticks, and culture media, etc., are not provided.


Test Organisms Reaction
Pseudomonas aeruginosa

ATCC® 27853
Oxidase-positive; blue/purple color develops within 10-20 seconds
Escherichia coli

ATCC® 25922
Oxidase-negative; no color development within 10-20 seconds

User Quality Control

It is recommended that each new lot or shipment of reagent be tested with known positive and negative controls.(3,8)


Oxidase Powder should appear beige in color. OxiDrop™, Oxidase Test should appear clear, and slightly brown in color.

Positive Oxidase Test

Pseudomonas aeruginosa (ATCC® 27853) applied to filter paper moistened with OxiDrop™ (Cat. no. Z119) reagent. The development of a blue/purple color within 10-20 seconds was indicative of a positive oxidse test.

Negative Oxidase Test

Escherichia coli (ATCC® 25922) applied to filter paper moistened with OxiDrop™ (Cat. no. Z119) reagent. No development of a blue/purple color within 10-20 seconds was indicative of a negative oxidse test.


1. Jorgensen., et al. Manual of Clinical Microbiology, American Society for Microbiology, Washington, D.C.

2. Tille, P., et al. Bailey and Scott's Diagnostic Microbiology, C.V. Mosby Company, St. Louis, MO.

3. Centers for Medicare and Medicaid, Appendix C, Survey Procedures and Interpretive Guidelines for Laboratories and Laboratory Services. Subpart K - Quality System for Non-Waived Testing. 493;1200-1265. www.cms.hhs.gov/clia.

4. Koneman, E.W., et al. Color Atlas and Textbook of Diagnostic Microbiology, J.B. Lippincott Company, Philadelphia, PA.

5. MacFaddin, J.F. Biochemical Tests for Identification of Medical Bacteria,, Lipincott Williams & Wilkins, Philadelphia, PA.

6. Isenberg, H.D. Clinical Microbiology Procedures Handbook, Vol. I, II & III. American Society for Microbiology, Washington, D.C.

7. Holt, J.G. and N.R. Krieg. 1984. Bergey's Manual of Systematic Bacteriology, Vol. I. Williams & Wilkins, Baltimore, MD.

8. Commission on Laboratory Accreditation, Laboratory Accreditation Program Microbiology Checklist. College of American Pathologists. Rev. 9/30/2004.

ATCC is a registered trademark of the American Type Culture Collection.