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.