Question

1. a bubble in the durham tube means: a. glucose was oxidized b. acid is present c. co₂ or gas was produced d. the media expired 13. if the broth remains red after incubation, it suggests: a. strong fermentation b. no fermentation c. salt intolerance d. sulfur reduction 14. the ph indicator in phenol red broth is: a. methyl red b. bromothymol blue c. phenol red d. crystal violet 15. what might happen to phenol red broth if it’s incubated too long? a. it becomes more acidic b. it turns black c. proteins are deaminated, leading to false alkaline results d. the durham tube dissolves

Explanation:

1. A Durham tube is used to detect gas production in a fermentation medium. A bubble indicates that $CO_2$ or other gas has been produced during the fermentation process.
2. Phenol - red broth is a differential medium. If it remains red after incubation, it means there has been no fermentation. Fermentation would produce acids which would turn the broth yellow.
3. The name of the broth 'phenol red broth' indicates that the pH - indicator in it is phenol red.
4. If phenol red broth is incubated for too long, proteins in the medium can be deaminated. This deamination can lead to the production of ammonia, which makes the medium alkaline and gives false alkaline results.

Answer:

1. C. $CO_2$ or gas was produced
2. B. No fermentation
3. C. Phenol red
4. C. Proteins are deaminated, leading to false alkaline results