VU Lab M5: Carbohydrate Fermentation

Virtual Unknown Software:  

For the best results on these labs, do the exercises in order and do not skip any exercises.  The
exercises build and if you skip any, there is a good chance you will be lost and overwhelmed with the
later activities.  Be sure to use the instructor-developed directions, not the directions supplied by the
program company.

Lab M5 Activities:

1. Open the Virtual Unknown software.

2. Review the procedures covered in the previous exercises.  As you learn new procedures,
it may help to make index cards for future reference.

3. Select a new unknown (click on the “New” button with the orange biohazard symbol) with the
Media Tests 3 (make sure to pick #3 and not a different number or these directions
won’t work correctly!!).

    * Give the unknown a name you will remember (no spaces).

    * Do NOT click auto-inoculation (this will show up on your lab report so be sure you don’t click it).

4. Read through the case study and assign the
Gram Stain status.

5.  In this lab we will start to explore some of the carbohydrate fermentation tests used to
determine the identification of unknown organisms.  

6.  Using the tube to tube procedure used in previous exercises, perform the following tests on this
 Phenol Red Glucose Broth Durham Tube, Phenol Red Lactose Broth, Phenol Red
Sucrose Broth, Phenol Red Mannitol Broth

NOTE: You can put more than one culture tube in the incubator before clicking “New Day”
– just make sure to label the tubes well so you don’t get them mixed up when you pull them out.

7.  Identify your unknown as
Salmonella typhii. (If this organism is not in the list, you most likely
made an error in recording the results for one of the above tests).  

8.  Review your lab report for errors and save the report to upload.

9.  Repeat steps #3-6 above selecting a new unknown with the subgroup
Media Tests 5.

10.  Identify your unknown as
Staphylococcus aureus.

NOTE:  If you get an "All microbes eliminated" error, watch this video for corrections:

11.  Review your lab report for errors and save the report to upload.

Questions:  Answer the following questions in a Word document and upload the document to
the correct dropbox, along with your .pdf lab reports saved from the VU program.  Both the
.pdf reports AND the question answers must both be uploaded for the lab to be graded.  
PDF reports must show that they were completed during this term (noted in the bottom left
corner of the report) and by the person submitting the report for a grade (noted in the top left
corner of the report).

1.   Case Study Number (click View --> Case Study to see the number): Media Tests 3:  ________  
and Media Tests 5: _________

2. Carbohydrate fermentation tests typically use media that contain a pH indicator such as
phenol red.  Explain the purpose of a pH indicator and the conditions under which phenol red
turns yellow and turns magenta.  (This may require some research).

3.  The metabolism of four sugars were tested in this lab exercise: glucose, lactose, sucrose, and
mannitol.  Research these sugars and describe one characteristic of each structure that makes them
unique from the others.  (This must be in your own words – do not copy and paste).

4.  Open your two lab reports from this lab and compare them side by side.  Which test results were
the same?  Which test results were different?  Were any of the test results not helpful (did not
eliminate any organisms)?  If so, which one(s)?

5.  Based on your answers for question numbers 3 and 4 above, and your knowledge of cell
structures used for metabolism, why might organisms that can metabolize some sugars not be
able to metabolize them all?

6.  At the end of all of the tests, how many organisms were remaining for the Media Test 3 sample?
_____________ for the Media Test 5 sample? ______________

7.  Is it possible to fully identify an unknown using only phenol red carbohydrate tests?  Explain your