Micro Lab Flashcards
What does crystal violet do?
Dyes Gram + bacteria purple
Why is iodine needed after adding crystal violet?
It helps fix the crystal violet to the Gram + cell walls
Why after adding iodine is the slide washed with acetone/alcohol?
This happens in order for the excess crystal violet to be removed from gram negative cells
What does safranin do to bacteria?
It stains Gram - cells pink
MacConkey agar
Has crystal violet and bile salts to prevent the growth of Gr - bacteria
Way to only grow Gr + bacteria
Contains lactose and neural red dye
Therefore lactose fermenting bacteria will produce acids (lactic acid) to lower the pH.
Neural red is the pH indicator for when it drops.
The bacteria will have pink rings around them if they ferment lactose.
The bile salts will precipitate from this pH change which causes the pink halo around the colonies
Mannitol Salt Agar
Selective isolation for Staph species
Contains 7.5% NaCl which prevents many Gr - and Gr + bacteria from growing
Staph aureus can grow!
Contains mannitol as carbon source and phenol red as the pH indicator
If the bacteria can ferment mannitol then the pH will drop from the excess acid produced and the red will turn yellow
Will turn pink if pH is above 8.4
Will remain red if pH is 6.9-8.4
Will turn yellow if pH is below 6.9
What can be accomplished with the use of fermentation tubes in identifying bacteria?
A way to see if a bacteria ferments the molecule (carbohydrate) in the tube
Can do lactose fermentation, glucose fermentation…etc…
We are using phenol red fermentation, turns yellow if acid is produced from active fermentation by the bacteria
What is the purpose of a Durham tube in a fermentation tube?
They collect gas (H2 or CO2) which can be produced during fermentation
