Why don t microorganisms in cultures exhibit constant exponential growth

“Lab 2 Culturing & Aseptic Technique BIO250L”

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Access Code (located on the underside of the lid of your lab kit): Click here to enter text.

“Pre-Lab Questions”

1. Proper aseptic technique is crucial to ensuring growth of pure bacterial colonies. What is one experimental way you can test your practices to confirm that you are using proper aseptic technique? Click here to enter text.

2. In a laboratory setting, what are three ways you can properly sterilize culturing equipment?

a. Click here to enter text.

b. Click here to enter text.

c. Click here to enter text.

3. For each inoculation tool, give one scenario in which use of that tool would be appropriate. Click here to enter text.

4. Why don’t microorganisms in cultures exhibit constant exponential growth? What are some steps you could take to extend the lifespan of a microbial culture? Click here to enter text.

5. Using a textbook or a reputable online source, describe how lab cultures are maintained in a continual pattern of growth. Focus particularly on those used in biotechnology, such as E. coli, which is used to make human insulin. Click here to enter text.

6. Which of these has a constant growth pattern: an open system or a closed system? Click here to enter text.

7. A human patient represents what kind of system for bacterial infections? Click here to enter text.

8. You’re a physician trying to isolate bacterial colonies from the human gut in attempt to diagnose a gastrointestinal infection. You streak your sample on a growth media containing glucose, amino acids, and salts that contain both sulfur and phosphorous with a pH of 7. You incubate the plates in aerobic conditions at 37 ˚C for three days, at which point you can see clear bacterial colonies forming on the plate. Would you feel confident in stating that you had successfully cultured all the bacteria from your gut sample? Why or why not? Click here to enter text.

“EXPERIMENT 1: Agar Plate Preparation and Bacterial Inoculation

Data Tables
Table 1: Experiment 1 Colony Growth

Plate Number

Source

Growth

(Color, Amount, Shape, etc.)

1

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2

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3

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4

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5

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Post-Lab Questions
1. Do some research and try to identify one to three types of microbes cultured on your plates. Using any resources available to you (i.e., a textbook or internet sources such as the CDC website), look up what bacteria are usually found on the areas from which you obtained your samples and the morphological characteristics of their colonies. Describe what morphological traits (i.e., size, shape, arrangement, color, margin, etc.) led to your hypothesized species identification. Be as specific as possible in the microbe type. Click here to enter text.

2. For the colonies hypothesized in Question 1, specify which plate and source the microbes came from. Are you surprised to find this type of microbe on this surface? Click here to enter text.

3. Looking at your control, did you perform proper aseptic technique or were your plates contaminated? If contamination did occur, list the possible sources and how you can prevent contamination in the future. Click here to enter text.

4. Was there a large risk for airborne contamination of your experimental plates? Based on the colonies that grew on your plates, do you think any of your experiment plates received airborne contamination? Click here to enter text.

Insert a photo of your plates after incubation. Include your name and access code handwritten in the background of your photo.

“EXPERIMENT 2: Bacterial Transfer to a Stab Tube and an Agar Plate

Data Tables
Table 2: Initial Reserved Plate Colony Growth Observations

Plate Sample

Appearance (morphology, etc.)

1

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2

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3

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Table 3: Final Plate and Stab Tube Growth Observations

Sample

Form

Growth (Yes or No)

Same Appearance as Initial Plate (Yes or No)

Successful Transfer? (Yes or No)

1

Plate

1

Stab Tube

2

Plate

2

Stab Tube

3

Plate

3

Stab Tube

Control

Plate

Control

Stab Tube

Post-Lab Questions
1. Were all of your colony transfers successful? Explain what could have been the cause of any unsuccessful transfers. Click here to enter text.

2. Did you have any growth that was different in appearance from the initial plates? What might account for any differences in growth on the transfer plate/tube? Click here to enter text.

3. Describe why an unsuccessful transfer or growth of the transfer plate/tube differing from the initial plates would be a problem if this experiment were placed in a larger context (i.e., only one step in a longer experiment). Click here to enter text.

4. Do some research and describe two or three scenarios in which it would be preferable to use a stab tube vs. a growth plate. (Hint: What do bacteria use to help them move? Can motility be used to help identify many medically important pathogenic bacteria such as the Enterobacteriaceae?) Click here to enter text.

Insert a photo of your plates and stab tubes after incubation. Include your name and access code handwritten in the background of your photo.