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While trying to identify an unknown sample, you inoculate the culture twice on TSA plates and twice in TSI tubes. Both of the plates show that only one species is present. Explain why in one TSI tube the tube is yellow and the butt is yellow but in the other the TSI tube has a red slant and a yellow butt? Why did the same organism cause 2 different results?

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Tod Thiel
Tod ThielLv2
28 Sep 2019

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Related questions

can you guys help me with my bio lab, please. it will be due tomorrow

PROCEDURE:

- Elodea (an aquatic plant)

- 4 capped test tubes containing 30 ml of phenol red solution each

- beakers

- lamp

- drinking straw s

- aluminum foil

- test tube rack

1. Obtain and number four test tubes of phenol red either 1, 2, 3, or 4 using a wax pencil . Warning: Hold test tubes by their sides and not by their caps. The test tube caps are the “ slip cap ” type and consequently the glass tube can fall out if not held by hand.

2. Uncap one of the tube s and pour its contents into a small beaker. B low into this liquid using a drinking straw until its color changes to a yellow - pale orange. Return the liquid back into this tube and recap . Repeat with the other 3 test tubes.

3. Stuff a large piece of fresh Elodea into Tubes 2 and 4. Fresh Elodea are a brighter green and bushier than older Elodea .

4. Cover Tubes 3 and 4 with aluminum foil so that no light can enter.

5. Place entire rack containing four tubes under a bright lamp , positioning the neck of t he lamp so that it gives maximum exposure . Light should only penetrate the uncovered tubes (1 and 2).

6. Be sure each tube is tightly capped.

7. Observe tubes 1 and 2 throughout the lab period . After 9 0 minutes have passed , remove the aluminum foil from 3 and 4 and observe.

8. Record your observations in the table below.

9. When everyone in your group has recorded the results, clean up by pouring the liquid from the tubes into the waste disposal container and putting the Elodea into the red biohazard waste cans. R ub the wax pencil markings off with a paper towel, rinse the tubes and leave them by the sink. Thanks!

RESULTS:

tube# description color at 0' at 90'
1 light yellow yellow
2 elodea, light yellow magenta
3 nothing yellow yellow
4 elodea, no light yellow organe

. Why does the color change you observed in some of these tubes occur?

7. What do you think would happen to the tubes if they were allowed to sit overnight just as they are at the end of this experiment but with the lights turned off?

8. Why do you expect this to happen? (HINT: What other process goes on in cells that requires oxygen and produces carbon dioxide?)

.

You are working in a food safety lab and were given some samples to evaluate for microbial contamination. The particular sample you’re working with today is a potato purchased at local farmer’s market booth. This farm does not use organic growth techniques. You swabbed the potato and performed a T-streak on MacConkey agar. From this you isolated several different colony morphologies, but one was of particular interest. The colonies were round and very glossy. On MacConkey agar they develop a reddish color.

You amplified one of these colonies for further analysis.

1. You prepare a wet mount and observe the microorganism under high magnification. You find that it has a rod shape and is non-motile.

2. You inoculate a thiolglycolate tube with this organism and incubate it overnight. Results are shown below.

Growth in Thiolglycolate (it is cloudy all the way to the bottom)

3. You inoculate a BD Enterotube with your unknown isolate. The results are shown below.

1 2 3 5 6 7 8 9 11 12

Glucose Lysine Ornithine Adonitol Lactose Arabinose Sorbitol V/P Urea Citrate

Color Yellow Purple Yellow orange yellow yellow yellow red pink blue

Gas? Yes

Note: I left out chambers 4 and 10 since you have no experience reading them and interpreting the results. The organism is negative for Indole, H2S, Dulcitol, and PA.

 

Case Study 4

Name: ____________________________________

Questions:

1. How would you classify this organism based on oxygen tolerance?

2. What is the scientific name of your microbe?

3. Describe the process you used to come to this result.

4. Is this a microbe that would be expected on produce?

5. Is this microbe a pathogen? Is it an opportunistic pathogen?

Please answer questions at the end.

In this lab, you will add different volumes of “cell-free supernatant” (CFS) to fresh cultures of V. harveyi and observe bioluminescence. The CFS is prepared by culturing V. harveyi in liquid medium overnight, then separating the cells from the supernatant by centrifugation.

MATERIALS • overnight culture of V. harveyi in AB medium • fresh AB medium • 1 microcentrifuge tube • 3 glass culture tubes

PROCEDURE

1. This experiment will be performed with your lab group. Label the microcentrifuge tube and 3 glass cultures tubes with your group number. Also, label the 3 glass culture tubes as follows: “Media only,” “Cells+fresh media,” and “Cells+CFS.”

2. Using aseptic technique, pipet different volumes of fresh AB medium into the glass tubes as follows: 1 mL in the “Media only” tube, 800 ul in the “Cells+fresh media” tube, and 500 ul in the “Cells+CFS” tube.

3. Pipet 500 ul of the overnight culture into a microcentrifuge tube and centrifuge at maximum speed (>13,000 x g) for 5 min to pellet the cells.

4. After centrifugation is complete, transfer 300 ul of the cell free supernatant (CFS) from the microfuge tube to the glass tube labeled “Cells+CFS”. Be careful to avoid the cell pellet.

5. Remove the remaining supernatant from the microfuge tube using a micropipette and discard as culture waste.

6. Add 500 ul of fresh AB medium to the cell pellet in the microfuge tube and pipet up and down to resuspend until no clumps are visible.

7. Add 200 ul of the cell suspension to the “Cells+fresh media” tube and 200 ul of the cell suspension to the “Cells+CFS” tube. Note the time.

8. Place the 2 glass tubes containing cells in the 30 degree incubator/shaker.

9. After 1 hour and 2 hours, observe your tubes next to the “Media only” tube in a dark room. You will need to let your eyes adjust for at least 30 seconds (count to 30 slowly in the dark) before you can evaluate whether the cultures are luminescent or not. Also, make sure you try swirling the tubes in the darkroom and observe the tubes for a minute after you have stopped swirling. After the observation at the 1 hour time point, put your tubes back in the incubator shaker until the 2 hour time point.

10. Note your observations. At the end of the lab, place your tubes in the tube waste.

Questions

1. What were the expected results? Explain the rationale of the experiment. If you didn’t obtain the expected results, hypothesize why not and describe how the experiment could be improved.

2. What are differences between luminescence and fluorescence?

3. Why do V. harveyi cultures glow more brightly when swirled vigorously? Be specific.

4. Imagine you have a mutant V. harveyi strain that can’t synthesize autoinducer and another mutant V. harveyi strain that makes a defective luciferase. If you streaked both strains near (but not touching) each other on the same plate, would you expect to see light produced? If so, by which strain, where, and why?

5. You have two identical tubes of wild-type V. harveyi (with the same cell concentration in each tube) in fresh media. To one tube, you add CFS from a light-producing V. fischeri culture, and to the other tube you add an equal volume of fresh media. If both tubes of V. harveyi have the same light production, what can you conclude? Explain.

6. Many biomedical research labs study quorum sensing in V. fischeri or V. harveyi. How is studying light production in marine bacteria relevant to human health? List at least 3 different examples.

7. Why do you think it is important for bacteria to be able to control the expression of some genes based on the number of individuals present?

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