Practical II Flashcards
What does a nitrate reduction test used for?
Identify bacteria that are able to reduce NO3 (nitrate).
What is the first step in a nitrate reduction test?
Reactants A & B are added to nitrate.
The result of the first step in the nitrate reduction test is the solution turns red. What is the interpretation of these results?
Nitrate (NO3) is reduced to nitrite (NO2) which reacts with reagents A & B to form red ppt. This is called a +1.
The result of the first step in nitrate reduction is the solution does not turn color. What is the next step?
Add zinc. If the solution then turns red, this is considered a negative test. The organism did not reduce nitrate (NO3) to nitrite (O2). Zinc did that. Zinc reduced nitrate (NO3) to nitrite (NO2) which reacted with reagents A & B to form nitrite (NO2).
In the nitrate reduction test, After the addition of zinc, what is the interpretation of a solution that again does not change color?
Nitrate (NO3) had been reduced beyond nitrite (NO2). This is a +2 because:
NO3 = negative
NO2 = +1
More reduced forms (N2O, NO, N2 gas) are +2.
What are the 3 possible results in the nitrate reduction test?
Add reagents A & B:
- Turns red = +1 Nitrate was reduced to nitrite
- Does not turn red = add zinc
- Zinc does not turn solution red = +2 (organism had reduced nitrate (NO3) beyond nitrite (NO2)
- Zinc does turn solution red = negative (zinc reduced nitrate (NO3) to nitrite (NO2))
What is the result of the nitrate reduction test if reagents A & B turns the solution red?
+1 - Nitrate was reduced to nitrite
What is the result of the nitrate reduction test if reagents A & B do not turn the solution red
Unknown, must add zinc to check
What is the result of the nitrate reduction test if after the addition of zinc, the solution does not turn red?
+2 - organism had reduced nitrate (NO3) beyond nitrite (NO2)
What is the result of the nitrate reduction test if after the addition of zinc, the solution turns red?
Negative - zinc reduced nitrate (NO3) to nitrite (NO2)
What are the negative, +1 and +2 results in the nitrate reduction test?
Negative = reagents A & B don't change the solution to red but the addition of zinc turns the solution red (because zinc reduced nitrate (NO3) to nitrite (NO2). \+1 = reagents A & B change the solution to red. \+2 = reagents A & B and also zinc don't change the solution color (was reduced beyond nitrite (NO2).
In the nitrate reduction test, which tubes turn red?
Negative = reagents A & B don't change the solution to red but the addition of zinc turns the solution red (because zinc reduced nitrate (NO3) to nitrite (NO2). \+1 = reagents A & B change the solution to red.
In the nitrate reduction test, which tubes are clear?
+2 = reagents A & B and also zinc don’t change the solution color (was reduced beyond nitrite (NO2).
In the nitrate reduction test, what does the addition of zinc do?
It differentiates between a negative and +2 test.
Gram stain procedure
Crystal violet (purple) Iodine Alcohol wash Safranin (pink) Gram + purple Gram - pink
What is the result of a Gram stain?
Gram + = purple
Gram - = pink
What does MacConkey Agar select for?
Selects for Gram -
acid production from lactose fermentation
What does starch hydrolysis test for?
The presence of amylase (enzyme that breaks down starches)
What does the catalase test identify?
Production of the enzyme catalase which converts H2O2 to H2O and O2
What are the results of MacConkey Agar?
Since MacConkey Agars selects for Gram - bacteria:
Positive = colonies and media appear pink/purple
Negative = colonies and media appear white/yellowish
What are the results of starch hydrolysis?
Since starch hydrolysis tests for the presence of amylase:
Positive = iodine creates halo around around colonies
Negative = no halo
What are the results of the catalase test?
Since catalase is an enzyme that converts H2O2 to H2O and O2:
Positive: Bubbles produced after H2O2 is added
Negative: No bubbles after H2O2 is added
What does the MR/VP test indicate?
Which pathway is used for fermentation of glucose
What does the MR test indicate?
Generation of acid from glucose fermentation (pH < 4.4) (mixed fermentation)