Microbiology Lab Questions

Effects of raising pH of EMB agar to 7.8

1.  What would the consequence be of raising the starting pH of EMB agar to 7.8 (normal pH = 7ish)?  Would it alter the selective nature of the media, the differential nature of the media or both?  Would it be more or less sensitive (more = detects coliforms more easily, less = less likely to detect coliforms)?  Explain your answer.

2.  All bacteria are able to use citrate for energy or as a carbon source.  That being said, only some bacteria can grow on citrate media.  Explain why bacteria that can use citrate for energy and carbon may not be able to grow on this media. 

3.   Imagine that I made a phenol red broth with lactose instead of glucose or sucrose and inoculated it with all of the organisms used in this lab today.  Which ones do you think would turn yellow?  Can you predict if they would make a bubble?  Explain your answer. 

4.  In the SIM media, which ingredients could be eliminated if the medium were used strictly for testing for motility and indole production?  What if I were testing only for motility and sulfur reduction?

5.  One characteristic of Enterobacteriaceae is that they all ferment glucose. Coliforms, on the other hand, are only coliforms if they ferment glucose AND vigorously ferment lactose. Bacteria can be both an Enterobacteriaceae and a Coliform. 

a.  Which media do you look at to tell if the bacteria is able to ferment glucose?

b. Which media do you look at to tell if the bacteria is able to ferment lactose?

c.  Look at your results and answer the following questions.  Be sure to base this off of your results and NOT an internet search.

d.     Which of the bacteria are true members of Enterobacteriaceae?  Are there any that are not Enterobacteriaceae?

e.     Which of the bacteria are true Coliforms? Which are not coliforms?