Lab 4 Selective Media & Agar BIO250L”
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“Pre-Lab Questions”
- 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.
- Why is differential media typically inoculated with isolated colonies that have been previously
cultured on general growth media?
- 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.
Post-Lab Questions
- 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.)
- What are some other potential sources of starch-degrading bacteria?
- What component makes starch agar selective for starch-degrading bacteria?
- Why were each of the following steps performed in this experiment?
a. Serial dilution:b. Growth on the nutrient agar plates:
Post-Lab Questions
- What chemical in MSA confers selectivity? How?
2. What chemical makes MSA differential? How?
3. Why are the nutrient agar plates used in this experiment?
- 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?
EXPERIMENT 3: Selection and Differentiation of Body Inhabiting Gram-Negative Bacteria from
Liquid Samples
Experiment 3 Post-Lab Questions
- What types of bacteria are inhibited on MacConkey agar? What ingredient(s) in MacConkey agar
selects against those bacteria?
What ingredient(s) makes MacConkey agar differential?
- 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?
- 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.
- Use a reputable internet source to research and describe what variations of MacConkey agar
can be used to detect other species of bacteria.
- How would you verify that the colonies that grew on a MacConkey agar plate were Gram-
negative?
- 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?
