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You are working in a microbiology lab and would like to isolatea nitrogen-fixing microbe from the soil. Would you use a definedmedium or a complex medium? Explain. Since only nitrogen-fixingmicrobes can grow on your medium would you consider it a selectiveor differential medium? Explain. Would you expect your microbe togrow quickly on your medium? Why or why not?

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Reid Wolff
Reid WolffLv2
28 Sep 2019

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Related questions

A. Indicate whether the following descriptions apply to nutrient, defined, selective,

differential, or enrichment media. If the statement applies to more than one, indicate which ones.

Answers may be used more than once.

____________________ if you want to take an environmental sample and grow a wide variety of

bacteria, you would use this medium

____________________ blood agar is an example, because you can see whether or not microbes

produce substances that lyse red blood cells

____________________ you might make this medium with a specially-formulated salt mixture,

some vitamins, and a refined protein source like peptone

____________________ the lauryl tryptose broth that we used for the presumptive coliform test

is this type of medium- we used it to increase the chance of actually seeing the coliforms

B. Indicate whether the following procedures are best performed with liquid or solid media. If

the statement applies to both, say “both.”

_______________________ you can count colonies of microbes grown with this medium

_______________________ you can grow facultative anaerobes with this medium

_______________________ you can use a spectrophotometer to measure growth in this medium

_______________________ you can prepare this medium by autoclaving it prior to use

Pre-Laboratory Questions

1. Why do bacterial cultures need to be incubated, usually for at least 24 hours, before we can see evidence of bacterial growth that can be observed with the unaided eye?

2. In what ways are the media used in this investigation selective?

3. In what ways are the media used in this investigation differential?

4. Consider a mixture of bacterial species from the same genus, such as Staphylococcus. Some members of this genus are harmful pathogens, while others are not. Would a selective medium alone be a good tool to separate the harmful species from the non-harmful species? Explain your answer.

Post-Lab Questions

1. Would simply adding a pH indicator like phenol red to a general-purpose medium, such as nutrient agar, result in a medium that is selective, differential, both, or neither? Why or why not?

2. Why were you instructed to inoculate each plate with three separate streaks, one of each bacterial species, instead of combining all three species and streaking them all onto the plate together?

3. Blood agar and chocolate agar are commonly-used media in many clinical and research laboratories. Why do you think they were not included in your kit?

4. Were there any discrepancies between what you saw in your experiment and what you expected to see based on the lab manual and your readings in this section?

2. Which of the following would the MSA medium NOT be considered: Select one:

a. Complex medium

b. Chemically defined medium

c. Differential medium

d. Selective medium

3. If you took a swab from a patient and cultured it on a MSA plate, which of the following could be identified by just using this test? Select one:

a. Staphylococcus epidermidis

b. Escherichia coli

c. Staphylococcus aureus

d. Micrococcus luteus

4. If you streaked the 3 organisms in this lab on a PEA plate and after incubating for 2 days at 37 degrees Celcius nothing grew (but they did grow on a NA plate made at the same time and grown in the same conditions), which of the following is the most likely cause for this result? Select one:

a. The agar was toxic.

b. The beef extract was bad.

c. The temperature was too low.

d. Too much phenylethyl alcohol was used

. e. The temperature was too high.

5. Why is the NA plate inoculated in addition to the Columbia CNA with 5% sheep blood agar plate? Select one:

a. Used to compare growth on non-selective medium

b. Used as second selective medium

c. Used to promote hemolysis

d. Used because it is easier to see

e. Used as a practice plate

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