Lab12-Medical Microbiology- Part1– Differential Media/Biochemical Tests, Sp2012
(Set all of your margins to ½”)
Purpose: The purpose of this lab is to help you become a little familiar with some of the tests that can be typically performed in a clinical or research lab facility. These tests may help in determining a particular pathogen’s growth needs. There are several sections to this lab. Find each section and complete the “Preparing for Class” sections. Preparing for class - Day 1
Read in your lab manual about the following agar mediums: Blood Agar (pg 168), EMB Agar (pg 170), Mannitol Salt Agar (MSA)(pg 172) ), MacConkey Agar (pg 174), and PEA Agar (pg 176) to answer the following:
1. What does the blood agar select for? Blood agar allows distinction among bacteria based on their ability to lyse red blood cells (hemolytic activity). 2. What color is the blood agar? Blood red color.
3. What are the 3 types of blood agar results and how can you recognize them? Beta hemolysis, which is the complete lysis of red blood cells and hemoglobin. This results in complete clearing of the blood around the colonies. Alpha hemolysis refers to the partial lysis of red blood cells and hemoglobin. This results in a greenish-grey discoloration of the blood around the colonies. No hemolysis, sometimes called gamma hemolysis results in no change in the medium. 3. What color is the EMB agar? Dark blue colonies with green metallic sheen or pink. 4. What does the EMB agar select for? Gram-negative bacteria. 5. What bacteria can easily be differentiated on EMB agar? Gram-positive. How is it recognized? It contains the dyes eosin and methylene blue, which inhibit the growth of gram-positive bacteria. 6. What color is the Mannitol Salt Agar (MSA)? Yellow color change in surrounding media. 7. What does the MSA agar select for? It contains 7.5% sodium chloride, which selects for organisms that are halotolerant. 8. Which bacteria (that we have learned about in lecture) can be seen on MSA agar? The organism Staphylococcus aureus. How can it be recognized? Capable of mannitol fermentation, signified by the color change in the surrounding media. 9. What color is MacConkey Agar? Neutral red, and produce a pink color. 10. What does the MacConkey agar select for? Gram-negative bacteria. 11. What color is PEA agar? Small transparent colonies
12. What does the PEA agar select for? Isolation of obligate anaerobic bacteria. Class day 1:
14. We will be setting up the Selective/Differential Media plates for each group as follows: Each group will have one bacteria sample and will do streak plates on each of the 3 agar plates (EMB, PEA and MacConkey). Label the bottom of the plate with your culture name. Invert your plates and stack them in the 370C incubator. Take care with your technique because each group’s plates will be shared with every group in the class.
15. Each group will have 2 MSA plates. Divide them in half and place the following samples on these plates: Nasal swab
We will use sterile cotton swabs for the nasal sample and fomite sample. Use your loop for the culture samples. Label your plates, invert them and stack them in the 370C incubator.
16. Each group will have a Blood Agar plate. Swab the back one student’s throat (sterile cotton swab) and transfer the sample using streak plating method to the blood agar plate.
Class day 2:
Look at the results of your different media plates.
17. In the space below, diagram your plate results. Label plates and color where appropriate.
18. Fill in the following charts to help organize this information: | |Selects for… |Differentiate by |Color of agar |Important Bacteria | |Blood Agar...
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