Question

4. This medium would be used to test for 5. If, after incubation, the broth turned yellow and bubbles were seen in the Durham tube you would report the results as 6. Is it possible to see bubbles in the Durham tube if the broth does not turn yellow during the incubation? Yes or No

Answer 1

1)Carbohydrates.

It is a differential test medium used to differentiate gram negative enterobacteria based on the utilisation of a carbohydrate source.The medium usually contains peptone,a pH indicator called phenol red,a durham tube and one carbohydrate source ,ie either glucose,sucose or lactose.Here the carbohydrate is tested and if the bacterium ferments a sugar to acid a yellow color will develop.

2)Positive

Positive result is indicated by phenol red by changing the color in acidic surroundings of red-orange to yelllow and gar or bubble formation in the butt of the test tube and an acid reaction on the slant surface.Color change may only occurs when sufficient amount of acid is produced,as bacteria may utilize the peptone producing alkaline by products.At low pH levels,it turns the media yellow,whilw at higher pH levels it turns the media purple.

3)NO

No bubble is formed in the inverted durham tube when the result is negative,because bacteria does not produce gas from the fermentation of that carbohydrate present in the media.If the organism utilise the carbohydrate ,then it will produce air bubbles which is trapped inside the durham tube.