MICR 300 W2010 Questions for Laboratory Exercises

Questions Exercise 1 (6 points)

1. How do you clean the lenses after use?

2. What is the highest final magnification achievable with a light microscope?

3. In general, at what position should the condenser be kept?

4. Express the maximum resolution of the compound microscope in terms of micrometers (m).

5. If you are getting 400× magnification with a 40× high-dry objective, what is the power of the eyepiece?

6. Immersion oil must have the same refractive index as _______ to be of any value.

MICR 300 W2010 Questions for Laboratory Exercises

Questions Exercise 2 (8 points)

1. Give two reasons for heating the slide after the smear is air-dried.a.

b.

2. What is the disadvantage of applying too many cells to a smear?

3. Why are basic dyes more successful on bacteria than acidic dyes?

4. List three basic dyes that are used to stain bacteria.

5. What color would you expect S. aureus to be if the iodine step were omitted in the Gram-staining procedure? Explain.

6. What structure of the bacterial cell appears to play the most important role in determining whether an organism is gram-positive?

7. Why would methylene blue not work just as well as safranin for counterstaining in the Gram-staining procedure?

MICR 300 W2010 Questions for Laboratory Exercises

Questions Exercise 3 (11 points)

1. Why would safranin not work well as a counterstain for the Ziehl-Neelson stain?

2. Are acid-fast mycobacteria considered gram-positive or gram-negative?

3. Name two diseases in which acid-fast staining is of paramount importance.

4. What is the reason to combine S. aureus with acid-fast organisms such as M. phleii when performing an acid-fast staining technique?

5. Explain the function of water in spore staining.

6. Why is heat necessary in spore staining?

7. Assume that during the performance of this exercise you made several errors in your spore-staining procedure. In each of the following cases, indicate how your microscopic observations would differ from those observed when the slides were prepared correctly.

a. You used safranin as the primary stain and malachite green as the counterstain:

b. You did not apply heat during the application of the primary stain:

MICR 300 W2010 Questions for Laboratory Exercises

8. What would happen if you heat fixed the slide prior to capsule staining?

9. Explain the medical significance of a capsule.

10. Give example of a genus other than Streptococcus or Bacillus that produces a capsule.

MICR 300 W2010 Questions for Laboratory Exercises

Questions Exercise 4 (8 points)

1. How does true motility differ from Brownian movement?

2. What could happen if you would touch the bottom of the motility agar with your needle during inoculation?

3. Explain why the following steps are essential during subculturing:

a) Flaming the loop or needle prior to and after each inoculation.

b) Cooling the loop or needle prior to obtaining the microorganism.

c) Holding the test tube caps in the hand as opposed placing them on the bench top.

d) Flaming the neck of the tubes immediately after uncapping and before recapping.

4. How can you ascertain whether a culture grown on an agar slant is contaminated?

5. How could you explain if a four-quadrant streak plate culture shows more growth in quadrant IV than in quadrant III?

MICR 300 W2010 Laboratory Questions

Questions Exercise 5 (2 points)

1. On the minimal medium without glucose you observe very faint growth in the area where you deposited your bacterial culture. Account for this.

2. How would this experiment turn out if you would use an autotroph instead of E. coli? Explain.

MICR 300 W2010 Laboratory Questions

Questions Exercise 6 (6 points)

1. Define generation time.

2. When following bacterial growth, why is absorbance plotted instead of percent transmission?

3. Can generation time be calculated for any phase of the growth curve? Explain your answer.

4. What is occurring in a bacterial culture during the lag phase? During the exponential growth phase?

5. What is the significance of a k value?

6. What is meant by the turbidity of a culture?

MICR 300 W2010 Laboratory Questions

Questions Exercise 7 (11 points)

1. What is the function of the following agents in the media used in this experiment? Sodium thioglycollate:

Resazurin:

Agar in FTM:

2. Which temperature seems to be closest to the optimum temperature for pigment formation?

3. Differentiate between the following: Thermophile:

Mesophile:

Psychrophile:

4. Which organism seems to grow best in acid media?

5. Which organism seems to grow best in alkaline media?

6. Evaluate the salt tolerance of the organisms you tested in this experiment: Tolerates limited amount of salt:

Tolerates a broad range of salt concentrations:

MICR 300 W2010 Laboratory Questions

Questions Exercise 8 (6 points)

1. What causes a color change in MSA?

2. Blood agar plates are used to determine_____________________________?

3. What would media surrounding colonies of S. epidermidis look like on MSA plates?

4. What is/are the differential ingredients in MSA?

5. What is/are the selective ingredients in MSA?

6. Do the numbers of different types of colonies on TSA vary from MSA? If so, why? Explain.

MICR 300 W2010 Laboratory Questions

Questions Exercise 9 (3 points)

1. Define mycology.

2. Explain what it means when you say that a fungus is dimorphic.

3. What kind of hyphae did you see for each of the three molds?

MICR 300 W2010 Laboratory Questions

Questions Exercise 10 (4 points)

1. How does the pipeting exercise help you understand the importance of accurate pipeting using microliter volumes?

2. Why did you practice pipeting samples of various viscosities?

3. Describe a good technique for withdrawing samples using a variable volume micropipet.

4. When using the micropipets in the lab, what volume is being delivered when the following digits appear in the window of a P20 micropipet? A P200 micropipet?

085

MICR 300 W2010 Laboratory Questions

Questions Exercise 11 (7 points)

1. From your graph, what were the latent period and the burst size for the T4 phage in this experiment?

2. Why is this experiment termed a “one-step growth curve?”

3. In a bacteriophage growth curve, what happens during the latent period?

4. Why is the initial bacterial culture greatly diluted after the bacteriophage adsorption step?

5. How would you define burst size?

6. Why is the water bath for the top agar held at 45 C and not at 100 C, the melting point for agar?

7. How is the bacteriophage growth curve different from the bacterial growth curve that you generated in the experiment of exercise 6?

MICR 300 W2010 Laboratory Questions

Questions Exercise 12 (5 points)

1. What was the effect of UV exposure time on bacterial viability? Explain.

2. How would you set up the experiment if you wanted to determine the UV-exposure time required to kill all bacterial cells?

3. Is there a difference between NA and MM+Glu results obtained from the replica plated control sample? Why or why not?

4. Which UV exposure time resulted in the mosta. Auxotrophic mutations?

b. Cell death?

MICR 300 W2010 Laboratory Questions

Questions Exercise 13 (7 points)

1. What does the growth or lack of it indicate on each side of the following plates as recorded in Section A above?

a. Ampicillin plate (side marked with donor BB4)

b. Ampicillin plate (side marked with recipient pLEX5A)

c. Tetracycline plate (side marked with donor BB4)

d. Tetracycline plate (side marked with recipient pLEX5A)

2. How many doubly resistant colonies were found on the plate with 10 l of mixed culture?

3. How many doubly resistant colonies were found on the plate with 100 l of mixed culture?

4. Should the number of plasmid transfers increase with incubation time? Why or why not?

MICR 300 W2010 Laboratory Questions

Questions Exercise 14 (2 points)

1. If one observes two DNA fragments of the different sizes but of same intensity on a gel stained with ethidium bromide, what conclusion can be reached regarding the relative quantities of the two DNA bands (the large band and a small band)? Why?

2. Based on the results of your restriction enzyme digest, which restriction enzyme recognition sequence is present more on the DNA of the plasmid?

MICR 300 W2010 Laboratory Questions

Questions Exercise 15 (5 points)

1. Why is it necessary to dilute the soil sample before plating?

2. What type of colonies did you look for?

3. Was your isolate an antibiotic producer? Explain.

4. Is S. epidermidis or S. aureus more sensitive to antibiotics produced by soil microbes? What is the basis for your answer?

5. Suppose your primary isolation plate looked like this after the one week incubation period. What would you conclude about the colony designated by the arrow? Explain

MICR 300 W2010 Laboratory Questions

Questions Exercise 16

NOT PERFORMED

MICR 300 W2010 Laboratory Questions

Questions Exercise 17 (6 points)

1. Did you get the expected results for your controls? If your answer is no, provide a rational explanation for why your results did not turn out as expected.

2. Was your unknown sample positive or negative for the C. difficile toxin? Justify your answer in light of your control and unknown results.

For the following four questions imagine that you are not sure if your control reagents are working, so you do an assay to test your controls.

3. How would you interpret the following results? Make sure you provide a clear explanation for your reasoning:

Treatment CPEToxin control +

Antitoxin control +Toxin/Antitoxin control +

Cell control +

4. How would you interpret the following results? Make sure you provide a clear explanation for your reasoning:

Treatment CPEToxin control +

Antitoxin control -Toxin/Antitoxin control +

Cell control -

5. How would you interpret the following results? Make sure you provide a clear explanation for your reasoning:

Treatment CPEToxin control -

Antitoxin control -Toxin/Antitoxin control -

MICR 300 W2010 Laboratory Questions

Cell control -

6. How would you interpret the following results? Make sure you provide a clear explanation for your reasoning:

Treatment CPEToxin control +

Antitoxin control -Toxin/Antitoxin control -

Cell control -

MICR 300 W2010 Laboratory Questions

Questions Exercise 18 (5 points)

1. Were your percentages for each type within the normal ranges? Explain.

2. What are likely errors when performing this count for the first time?

3. Under what circumstances could you observe:

a. Neutrophilia:

b. Lymphocytosis:

c. Eosinophilia:

MICR 300 W2010 Laboratory Questions

Questions Exercise 19 (5 points)

A. Answer the following questions:1. How can you recognize whether your assay was technically well performed?

2. What was the highest/lowest lysozyme concentration in your class?

3. What parameters could influence the lysozyme concentration that is measurable with the lysoplate assay in individual saliva?

4. In what other ways could you present the class data?

5. What calculation can you use to evaluate how consistent your pipetting was?

MICR 300 W2010 Laboratory Questions

Questions Exercise 20 (4 points)

1. What do the circular precipitin rings represent?

2. Why do the ring sizes change until equilibrium is reached?

3. Predict the results if a very low concentration of antigen were placed into a well.

4. What would happen if not enough antibody was incorporated into the agarose?

MICR 300 W2010 Laboratory Questions

Questions Exercise 21 (9 points)

1. In general, what effect does alcohol have on the level of skin contaminants?

2. Why is it impossible to completely sterilize the human skin?

3. Which antibiotic would be suitable for the control of the following species?S. aureus:

E. coli:

P. vulgaris:

P. aeruginosa:

4. Differentiate between the following:Narrow spectrum antibiotic:

Broad spectrum antibiotic:

5. Which antibiotics used in this experiment would qualify as being excellent broad-spectrum antibiotics?