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Bacteria's fermentation ability
The ability or inability of a particular species to ferment a particular carbohydrate depends on the presence or absence of an enzyme system to convert that carb to glucose. Those that can ferment - have a variety of by products ( ex. acids, liguid, gases.) All bacteria that fermetn carbs the by product is always acid.
Phenol-Red(PR) Carbohydrate Fermentation Broths
- 1. Carbohydrates: contatin single carb.
- 2. Phenol Red: A pH indicator; yeloww -pH below 6.8, red - pH 6.8-7.4, pink -above pH7.4
- 3. Durhan Tube: produced gasses get trapped in this upside down tube.
What down "V" mean?
The result may be different everytime you run a test because bacteria doesnt' always give the same results. With single test - cannot absorve "v"
- if bacteria can reduce sulfur to hydrogen sulfide it will be visible as black precipitate.
- if bacteria ferments only glucose after 18hr the tube will be red and butt yellow.
- If glucose and lactose, or gulocse ans sucrose are fermented the enitre tube turn yellow
- if gas produced - cracked agar.
- + test = cloud, diffuse growth throughout the medium
- - test = well defined growth alon the stab only.
- to identify organisms tha produce the enzyme catalase.
- If catalase present, the added hydrogen peroxyde will be converted into water and O2 which escapes as a gas.