Question

1. What is the IMViC series of tests? How are the results interpreted?

2. TSI tests for fermentation of several sugars. Is it possible to differentiate between which sugars are fermented?

3. What is a selective media?

4. What is a differential media?

Answer 1

1. I- Indole Test; positive result is indicated by red layer at the top of the tube after addition of Kovac's reagent. Negative result is indicated by no colour change.

M- Methyl Red test; Positive test is indicated by development of red colour after addition of methyl red solution.

Vi- Voges Proskauer test; A positive test is indicated by development of red brown colour.

C- Citrate test; Positive test is indicated by growth and blue colour change.

2. Yes, if fermentation takes place, there will be production of gas and there will be change in pH which will result in colour change from red to yellow.

3. Selective Medi contain substances that inhibit all but a few types of bacteria and facilitate the isolation of a particular species. This media is used to isolate a particular bacteria from specimens where mixed bacteria flora is expected.

Examples: Deoxycholate citrate agar, Bile Salt Agar

4. When a media contains substances which help to distinguish different characteristics of bacteria, it is known as differential media.

Examples: MacConkey's agar, Lactose fermenters bacteria will form pink coloured colonies whereas non lactose fermenters will form colourless or pale colonies.