Microbiology 150 Lab 3-Selective vs. Differential Media

Topics: Growth medium, Bacteria, Microbiology Pages: 10 (2930 words) Published: February 1, 2013
Online BIO 150 Introductory Microbiology #3 Lab Report

NAME __ Lab Group 2_____

Answer the following questions as you work your way through the lab material typing in your answers. Then submit your finished lab report as a Microsoft Word document. This lab report is worth 100 points towards your final lab grade. Each Q is worth 2 points unless otherwise noted. Also, per the Honor Code, this work must be your own. This is due Mon. 10/8 at 11:59 PM. The theme of this lab is the identification of unknown bacteria and viruses in a lab.

Selective vs. Differential Media

Selective vs. Differential Media
Use the following website to help you answer Q 1 and 2

1. What is a selective medium? What makes the medium selective? Name 2 examples (3 pts.) A selective medium is a medium that contains antimicrobials, dyes or alcohol that supports the growth of certain organisms, while inhibiting the growth of others. Two examples of selective medium are Mannitol Salt agar and Phenylethyl Alcohol.

2. What is a differential medium? What makes the medium differential? Name 2 examples (3 pts.) Differential medium is distinguishing microorganisms from one another based on growth characteristics. A medium is differential when you are able to visibly see the differences in growth patterns of organisms. Differential media include blood agar and Eosin Methylene Blue.

Steps Used in Identifying an Unknown Bacterium in a Laboratory

I. In a lab situation you would take you inoculum and perform a streak plate in order to separate out individual cells enough to obtain a pure culture (see Atlas p. 5)
3. What is the most common streaking method? (2 pts.)
The most common streaking method is the Streak plate method, while the most common streaking technique is the quadrant method. The quadrant method incubates an agar using a four-streak pattern.

4. What is the principle behind the Streak Plate Method of Isolation? (2 pts.) The Streak Plate Method of Isolation is used to obtain a pure culture in order to isolate a certain organism. This method allows for the organism to produce individual colonies on an agar plate.

II. After incubating your streak plate you would perform a Gram Stain as you learned in Lab #1 – The Virtual Gram Stain. I'm directing you to the Virtual Gram Stain website from the Univ. of Michigan. Click on "View Example. You will need to move your cursor over the test tubes to see what each contains. Then click on the test tubes in the correct order to run the program - this is really cool! http://vudat.msu.edu/gram_stain/

5. What were the results of your Virtual Gram Stain, i.e. describe what you see on the slide as to color, Gram Stain result and morphology? (4 pts.) The gram stain was negative. The shape was bacilli and had purple spores present.

III. Using the dichotomous keys provided as MSWord Documents in this lab, you would carry out specific tests utilizing selective and differential media in order to identity your bacterium. In a microbiology lab you would use “Bergey’s Manual of Determinative Bacteriology”. This book includes all tests and their results to aid in the identification of unknown bacteria. Use the following websites to answer these questions: http://www.saskschools.ca/curr_content/biology20/unit3/unit3_mod1_les2.htm http://www.uiweb.uidaho.edu/micro_biology/250/IDFlowcharts.pdf

6. What is a dichotomous key? (4 pts.)
A dichotomous key is a key used to help identify bacteria using process of elimination testing in order to identify each bacteria characteristic.

7. Based on the Information Flow Charts from Bergey's Manual of Determinative Bacteriology Page 2, answer these questions: (4 pts) a. What is the FIRST test that is performed in a lab to differentiate between groups of bacteria? The first test preformed to differentiate between bacteria is...
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