Lab 4 Selective Media &
A
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gar
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IO250L”
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“Pre-Lab Questions”
1.
What is the difference between chemically defined and chemically complex media? Give either a clinical or environmental research example for which each media type would be the most appropriate choice for culturing microorganisms.
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2. Why is differential media typically inoculated with isolated colonies that have been previously cultured on general growth media?
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3. Use a textbook or a reputable internet source (such as www.cdc.gov) to research and describe a scenario in a lab or clinical setting in which a selective and/or differential test would be necessary.
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“EXPERIMENT 1: Bioprospecting for Starch
D
egrading Bacteria
Data Tables
Table 3: Starch Agar and Gram Iodine Results
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Sample
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Growth on Starch Agar? (Yes or No)
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Clear area around colonies?
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Do these bacteria contain amylase?
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Post-Lab Questions
1. Why is cow manure used as a potential source of starch-degrading bacteria? (If you are not familiar with the process of digestion in cows, use a reputable internet source to inform your answer.)
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2. What are some other potential sources of starch-degrading bacteria?
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3. What component makes starch agar selective for starch-degrading bacteria?
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4. Why were each of the following steps performed in this experiment?
a. Serial dilution:
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b. Growth on the nutrient agar plates:
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c. Streak on the starch agar plates:
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“EXPERIMENT 2: Selection and Differentiation of Body Inhabiting Gram-Positive Bacteria
Data Tables
Table 4: Experiment 2 MSA Growth Observations
Surface Tested
Growth (Yes or No) – Nutrient Agar
Growth (Yes or No) – MSA Agar
MSA color around colonies (Red or Yellow)
Other Observations
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Post-Lab Questions
1. What chemical in MSA confers selectivity? How?
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2. What chemical makes MSA differential? How?
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3. Why are the nutrient agar plates used in this experiment?
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4. Was there any growth on you MSA plates? Did any of the colonies change the color of the MSA? What does this tell you about the bacteria taken from each area of your body?
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EXPERIMENT 3: Selection and Differentiation of Body Inhabiting Gram-Negative Bacteria from Liquid Samples
Data Tables
Table 5: MacConkey Agar Results
Sample
Growth? (Yes or No)
Colony Color (Clear or Red)
Analysis
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Experiment 3 Post-Lab Questions
1.
What types of bacteria are inhibited on MacConkey agar? What ingredient(s) in MacConkey agar selects against those bacteria?
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2. What ingredient(s) makes MacConkey agar differential?
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3. Using a textbook and a reputable
online
source (such as
the CDC
), research and describe some potentially pathogenic members of the intestinal bacteria family Enterobacteriaceae. Which pathogenic species are lactose fermenters that will grow on MacConkey agar?
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4. Use a reputable internet source to research and describe some potentially pathogenic intestinal bacteria that do not ferment lactose that will grow on MacConkey agar.
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5. Use a reputable internet source to research and describe what variations of MacConkey agar can be used to detect other species of bacteria.
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6. How would you verify that the colonies that grew on a MacConkey agar plate were Gram-negative?
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7. Look up the formula for MacConkey agar either in a microbiology textbook or online. Is this a chemically defined or a chemically complex media? Why is that important?
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Lab 5 Eukaryotic Microbes, Parasitology, & Viruses BIO250L”
Student Name:
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“Pre-Lab Questions”
1. What is a model organism, and why is Saccharomyces cerevisiae so often used as one?
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2. Research and discuss the properties of mold that make them sometimes beneficial to humans, and sometimes potentially harmful.
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3. Parasitic helminths are a major cause of disease in undeveloped countries around the world. Discuss the role that microbiologists can and have played in helping to reduce the number of infections caused by parasitic helminths.
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“EXPERIMENT 1: Mold Growth on Bread and Fruit
Data Tables
Table 1: Experiment 1 Growth Results
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Condition
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Day of First Visible Growth
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Extent of Growth on Bread (Mean)
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Extent of Growth on Apple (Mean)
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Bright, Control
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Bright, Water
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Bright, Sugar
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Bright, Lemon
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Bright, Vinegar
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Dark, Control
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Dark, Water
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Dark, Sugar
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Dark, Lemon
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Dark, Vinegar
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Post-Lab Questions
1. Which condition produced the most mold growth? The least? The fastest? The slowest?
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2. What was the purpose of examining three pieces of bread and three pieces of apple in each treatment?
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3. Based on your results, what conditions are most favorable for mold growth on bread? On apple?
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4. Would these conditions apply to all fungal growth?
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5. Did you notice a difference in mold growth on the bread vs the apple? If so, what do you think might account for this difference?
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6. How would changing the type of bread (e.g. fresh from a bakery, no preservatives vs. prepackaged with preservatives) affect the results?
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7. How do you think changing the temperature at which the bags were incubated affected the results?
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8. How would you test the predictions/hypotheses from Questions 6 and 7?
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9. Look up the pH of lemon juice and vinegar. Based on your results and your knowledge of favorable environmental conditions for fungal growth, what can you conclude about the effect of pH on growth?
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10. What is the source of the mold that grew on the samples?
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“EXPERIMENT 2: Microscopic Observation of Saccharomyces Cerevisiae
Post-Lab Questions
1. What information/structures were you able to glean from the Gram stain that you could not get from the methylene blue stain?
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2. What information/structures were you able to glean from the methylene blue stain that you could not get from the Gram stain?
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3. Is Saccharomyces cerevisiae Gram-positive or Gram-negative? Research and describe the composition of yeast cell walls. How does the composition compare to the cell walls of Gram-positive or Gram-negative bacteria?
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