9.4: MAC Media Procedure
MacConkey Media Procedure
Name: _____________________________________________________
Course Section: ______________________________________________
The following activity will teach students how to inoculate an MAC agar plate. Post-inoculation, students will use their colony growth to determine if the bacteria are gram positive or gram negative and the bacterial rate of lactose fermentation.
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| Procedure | |
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Step 1:
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| Procedure |
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Step 2:
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Step 3:
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Step 4:
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Results
In table below, record your observations for colonies grown on MAC media.
| Results Table | ||||
| Bacterial Species | Gram Positive or Negative | Colony/Media Color | Rate of Lactose Fermentation | |
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Escherichia coli
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Serratia marcescens
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Staphylococcus epidermidis
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General Questions
1. What adaptation allows enteric bacteria to survive in the human gut?
2.How does MacConkey agar inhibit the growth of gram positive bacteria?
3. Why does lactose fermentation change the color of the bacteria colonies and the MAC media?
4. You grow an unknown species of bacteria on an MAC plate. The colonies turn a white color while the media turns yellow. What kind of lactose fermenter is your unknown species?
Health-Related Questions
1. P. aeruginosa bacteria target which group of people?
2. Why is it important that a patient submit a clean urine sample when trying to determine if their UTI is caused by P. aeruginosa ?
3. You collect a urine sample from a patient with a UTI and culture the sample on an MAC plate. The bacteria grow in blue-green colored colonies, but there are no changes to the media color. Would you classify this UTI as being caused by P. aeruginosa ? Explain your answer.
Attributions
"Microbiology Labs II: Results, 12.6.1 MacConkey Agar" by Dr. Gary Kaiser , LibreTexts: Biology , Community College of Baltimore County, Catonsville Campus is licensed under CC BY 4.0
"Microbiology Labs II: Pure Cultures, 3.4 Use of Specialized Media" by Dr. Gary Kaiser , LibreTexts: Biology , Community College of Baltimore County, Catonsville Campus is licensed under CC BY 4.0
"Bio 221 Lab: Physiological Tests, 22.2 Selective and Differential Media-MacConkey, EMB, MSA" by Kelly Burke , LibreTexts: Biology , College of The Canyons is licensed under CC BY