What does a negative indole test mean?
It is used to determine the presence of the enzyme tryptophanase. Tryptophanase breaks down tryptophan to release indole, which when reacts with cinnamaldehyde produces a blue-green compound. The absence of enzyme results in no color production (i.e. indole negative).
What color is a negative indole test?
light pink
Expected Results. Positive: A positive reaction is denoted by the appearance of a blue to blue-green color change on the bacterial smear within 2-3 minutes. Negative: Negative reactions remain colorless or light pink. Note: Positive reaction is Red-violet in the case of Providencia alcalifaciens.
What does a positive indole result mean?
The presence of indole when a microbe is grown in a medium rich in tryptophan demonstrates that an organism has the capacity to degrade tryptophan.
What is the conclusion of indole test?
Conclusion: The Indole positive test indicates that the given organism contains tryptophanase whereas, the indole negative test indicates that given organism lacks tryptophanase.
What does the indole test determine?
The indole test is a biochemical test performed on bacterial species to determine the ability of the organism to convert tryptophan into indole. This division is performed by a chain of a number of different intracellular enzymes, a system generally referred to as “tryptophanase.”
Which bacteria is indole positive?
Bacteria that test positive for cleaving indole from tryptophan include: Aeromonas hydrophilia, Aeromonas punctata, Bacillus alvei, most Citrobacter spp., Edwardsiella spp., Escherichia coli, Flavobacterium spp., Haemophilus influenzae, most Proteus spp.
Which of the following is indole negative?
Bacteria which give negative results for the indole test include: Actinobacillus spp., Aeromonas salmonicida, Alcaligenes sp., most Bacillus sp., Bordetella sp., Enterobacter sp., most Haemophilus sp., most Klebsiella sp., Neisseria sp., Mannheimia haemolytica, Pasteurella ureae, Proteus mirabilis, P.
Can E. coli be indole negative?
Indole production is often used to differentiate E. coli from other indole-negative enteric bacteria because 96% of E coli are indole positive, whereas many enterobacterial species are negative in the indole reaction.
Is Pseudomonas indole positive?
Pseudomonas gives negative Voges Proskauer, indole and methyl red tests, but a positive catalase test.
Is E. coli indole-negative?
Is Staphylococcus indole positive?
In the Gram-positive Staphylococcus aureus, indole decreased production of the virulence factor staphyloxanthin,33 which confers enhanced oxidant and neutrophil resistance to the bacterium, and has been shown to contribute to virulence in vivo.
Is E. coli indole positive?