About Oxidase test which of the following is true?
AEnterobacteriaceae is oxidase negative
BPseudomonas and Vibrio are oxidase positive
CNeisseria are Oxidase positive
DAll the above are true
Answer:
D. All the above are true
Read Explanation:
Principles of the Oxidase Test
- The Oxidase test is a fundamental biochemical assay used in microbiology to identify bacteria that produce the enzyme cytochrome c oxidase.
- This enzyme is a key component of the bacterial electron transport chain (ETC), facilitating the transfer of electrons to oxygen, the final electron acceptor in aerobic respiration.
Mechanism and Procedure
- The test utilizes an artificial electron donor, most commonly tetramethyl-p-phenylenediamine (TMPD) dihydrochloride.
- When cytochrome c oxidase is present, it catalyzes the oxidation of the TMPD reagent, resulting in the formation of an intensely colored compound known as indophenol blue.
- Positive Result: The colony or smear turns dark purple or black, usually within 5 to 10 seconds.
- Negative Result: No color change occurs, or the color change happens only after 60 seconds (which is considered a false positive or negative result depending on protocol).
Diagnostic Significance in Microbiology
- This test is widely used to differentiate between major groups of Gram-negative bacteria.
- Oxidase Positive Genera: This group includes Pseudomonas, Neisseria, Vibrio, Campylobacter, Aeromonas, and Moraxella.
- Oxidase Negative Genera: Crucially, members of the Enterobacteriaceae family, including Escherichia coli, Salmonella, Shigella, and Klebsiella, are oxidase-negative.
- Using a metal inoculating loop containing iron can lead to false-positive results; therefore, platinum loops or wooden sticks are recommended for performing the test.