What does a positive and negative indole test look like?

Indole Spot Reagent Result Positive reaction: The development of a blue colour within 3 minutes. Negative reaction: The development of a pink colour within 3 minutes.

What does a positive indole test mean?

A positive indole test is indicated by the formation of a red color in the reagent layer on top of the agar deep within seconds of adding the reagent. If a culture is indole negative, the reagent layer will remain yellow or be slightly cloudy.

Is E coli indole positive or 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.

What bacteria can produce indole?

many pathogenic bacteria such as Bacillus alvei, pathogenic E. coli, several Shigella strains, Enterococcus faecalis, and V. cholerae, can produce indole.

What does a positive indole test look like?

A positive result is shown by the presence of a red or red-violet color in the surface alcohol layer of the broth. A negative result appears yellow. A variable result can also occur, showing an orange color as a result.

Is Salmonella indole positive?

Salmonellae yield negative Voges-Proskauer and positive methyl red tests and do not produce cytochrome oxide. Salmonellae are also unable to deaminate tryptophan or phenylalanine and are usually urease and indole negative. Based on the biochemical tests above, Salmonella can presumptively be identified.

Is E coli oxidase positive?

E. coli bacteria are among the few species of lactose (LAC)-positive, oxidase-negative, gram-negative rods that are indole positive.

Is E. coli oxidase positive?

How can you tell if your SIM test is positive for motility?

A diffuse zone of growth flaring from the line of inoculation indicates a positive motility test. The absence of such growth or its confinement to the stab line is indicative of a negative motility test. If H2S-producing bacteria obscure the butt of the tube, assume this is a positive motility reaction.

Is Salmonella Mr positive or negative?

Biochemical Test and Identification of Salmonella Typhi

Is Salmonella H2S positive or negative?

enterica to produce hydrogen sulfide (H2S) is an important phenotypic characteristic used to screen and identify Salmonella with selective medium; however, H2S-negative Salmonella have recently emerged.