Motility Test Media
Sample Questions
 | Which tube(s) contain motile organisms? |
| What does the tetrazidium dye do in the media? |
| Is this a differential, enrichment and/or selective media? |
| What can be done to confirm motility (i.e. another test, or or another way of determining motility)? |
From left to right: motile, non-motile, motile
MR/VP Test
Sample Questions
|
How is this test performed? |
|
What reagents are added? |
|
Which tubes are
positive and which are negative for MR test? |
From left to right: MR negative, MR positive
Nitrate Test Step 1
Sample Questions
|
How is this test performed? |
|
What reagents are added? |
|
Which tubes are positive and which are negative for nitrate reduction for Nitrate reduction? |
Tube A contains the nitrate broth with growth and no reagents. The reagents dimethyl-alpha-naphthylamine and sulfanilic acid were added to tubes B and C. Tube B shows a positive result for nitrite (nitrate reduction has occurred) and tube C shows a negative result for nitrite (nitrate reduction may or may not have occurred).
Nitrate Test Step 2 (Confirmatory)
Sample Questions
|
How is this test performed? |
|
What reagents are added? |
|
Which tubes are positive and which are negative for nitrate reduction for Nitrate reduction? |
We must confirm the results from Tube C above. Tube C may not contain an organism that is negative for nitrate reduction. It is possible that the organism growing in tube C reduced nitrate to ammonium. If zinc powder is added to a tube that showed a negative result for nitrite (as tube C did above) this will tell us if there is nitrate left in the tube. If nitrate is still present then indeed the organism does not reduce nitrate. Zinc powder was added to these tubes, which contain different organisms grown in nitrate broth. The tube on the left shows that nitrate is still present so that organism is not a nitrate reducer. The tube on the right shows that nitrate is no longer present so the organisms must be a nitrate reducer.
MacConkey Agar
Sample Questions
| What does MacConkey agar test for? |
| What does the result at the top of the plate mean? |
| What does the result at the bottom of the plate mean? |
| If something did not grow at all on MacConkey what does that mean? |
The organism growing at the top is a Gram negative organism that does not ferment lactose. The organism growing at the bottom is a Gram negative organism that does ferment lactose.
Urea Broth
Sample Questions
|
What does this media test for? |
|
What types of organisms can hydrolyze urea? |
|
Which tube is showing a positive result? |
The tube on the left is a urease positive organism and the tube on the right is a urease negative organism.
EMB Agar
Sample Questions
| What does EMB agar test for? |
| Does the top plate contain a pure culture? |
| What do these results mean? |
Each of these plates contain Gram negative organisms that can ferment lactose. The top plate is contaminated. Notice the white colonies interspersed with the pink colonies. When organisms ferment the lactose in EMB they produce acid which turns the colonies pink, purple or green, depending on the pH.
Sheep's Blook Agar Plate (BAP)
Sample Questions
| What does BAP agar test for? |
| What do these results mean? |
This media is used to test if an organism has hemolysins (enzymes that lyse red blood cells). If an organism lyses red blood cells in the media then clearing zones are produced around the culture. An organism can be classified as alpha, beta or gamma hemolytic. The culture on the top portion of this plate is showing alpha hemolysis (partial clearing of red blood cells). The culture on the bottom of the plate is showing gamma hemolysis (no clearing of the red blood cells).
Triple Sugar Iron Slant (TSI slant)
Sample Questions
| What does TSI test for? |
| What do these results mean? |
TSI slants are used to test if an organism ferments glucose and sucrose and/or lactose and if the can reduce sulfate. The tube on the far left is uninoculated. The second tube shows a yellow butt and a yellow slant. This means the organism fermented glucose and lactose and/or sucrose. The third tube has a yellow slant and a yellow butt. This means that the organism fermented glucose and lactose and/or sucrose and reduced sulfate. The fourth tube from the left shows a yellow butt and a red slant. This means that the organism only fermented glucose. The last tube shows zero fermentation, but shows a positive result for sulfate reduction.
