Lab 2 Flashcards
How can we identify a negative motility from the SIM media test?
Negative test is indicated by growth being along the inoculation path. (well-defined inoculation path.)
What metabolic process could bacteria have if they are positive for S in SIM test?
Sulfur reduction
What metabolic process do bacteria have if they are positive for I in SIM test?
Indole production (the hydrolysis of tryptophan to indole, pyruvic acid, and ammonia)
What do bacteria have if they are positive for M in a SIM test?
They have a motility organelle. Most commonly a flagella.
What enzyme is responsible for urea hydrolysis?
Urease
What color indicates a positive urea hydrolysis test?
Bright pink (fuchsia)
What is the pH indicator used in the urea hydrolysis test?
Phenol red
What happens to the pH when urea is hydrolyzed?
The pH increases due to ammonia production
What enzyme mediates nitrate reduction?
Nitrate reductase
What does a red color indicate after adding reagents A and B in the nitrate reduction test?
Positive result for nitrate reduction (NO3 to NO2)
During nitrate reduction test; what does no color change after adding reagents A and B indicate?
Nitrate was not reduced or was fully reduced beyond nitrite
Why is zinc added in the nitrate reduction test?
To check if nitrate is still present by forcing its reduction to nitrite
During a nitrate reduction test; what does a red color after adding zinc indicate?
Negative result for nitrate reduction (nitrate was not reduced by the organism)
In a nitrate reduction test; what does no color change after adding zinc indicate?
Positive result for complete nitrate reduction (beyond nitrite)
What is the purpose of the nitrate reduction test?
To determine if bacteria can reduce nitrate (NO₃⁻) to nitrite (NO₂⁻) or other nitrogenous compounds using nitrate reductase.
What enzyme mediates nitrate reduction?
Nitrate reductase.
What does a red color indicate after adding reagents A and B in the nitrate reduction test?
A positive result, meaning nitrate was reduced to nitrite.
What happens if no color change occurs after adding reagents A and B, during a nitrate reduction test?
The bacteria either did not reduce nitrate or reduced it further beyond nitrite.
What is the purpose of adding zinc in the nitrate reduction test?
To determine if nitrate was still present in the broth, indicating a negative result if it turns red.
In a nitrate reduction test; what does it mean if no color change occurs even after adding zinc?
The bacteria reduced nitrate to nitrogen gas or other nitrogenous compounds, indicating a positive result.
What does “MR” mean from the MR-VP lab?
Methyl red
What does “VP” mean from the MR-VP lab?
Vogues-Proskaurer
What is the MR test testing for?
Mixed-acid fermentation pathway. Causing a significant decrease in the pH.
Why does the mixed-acid fermentation pathway significantly reduce the pH of the medium compared to other acid producing metabolic pathways?
Because it produces 4 moles of acidic products to every 1 mole of glucose fermented.
