microbiology lab questions

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Chapter #25 Bacterial culture characteristics 1. After the incubation period why is it best to refrigerate culture plates and tubes rather than storing them at room temperature? 2. How can you account for the observation that a mass or colony of bacteria shows pigmentation while the individual cells have transparent cytoplasm? 3. Describe the factors that may alter the expression of the cultural characteristics of bacteria? 4. Determine which cultural characteristics noted in this exercise are more distinctive than others . 5. Suppose your unknown prefers to grow at 75C, yet both slants show similar growth. Provide some reasons to account for this observation . Chapter #24 Bacterial Structural Characteristics 1. Describe several instances, other than those in the introduction to this exercise, where identification of a bacterial unknown is bacterial and necessary. 2. Which structural characteristics in this exercise were most helpful in narrowing the identification of the unknown bacterium? Which tests were least helpful? Why? 3. Before doing the spore stain, what information from the Gram stain results may assist you in a preliminary determination for the presence of spores? 4. What other structural characteristics can be assumed with a positive motility test? 5. What other bacterial structural characteristics could be useful with the light microscopes in eventual identification of species? Chapter# / Pure culture techniques 1. Explain several advantages of the streak plate technique over the pour plate technique, and several reasons why the pour plate technique might be preferred to the streak plate technique. 2. Predict the out come of incubating inculcated streak and pour plates in the upright rather than the inverted position. 3. What variations might be made in the isolation techniques if molds were to be isolated from a mixed culture? 4. While performing the pour plate technique, a student inadvertently dipped a hot loop into agar tube #1 to obtain bacteria for agar #2. What will result?? 5. Explain how isolation methods might be useful in determining the purity of a bacterial culture? Chapter #6 The Gram Stain Technique 1. Why is the Gram Stain Technique More Valuable than the simple stain technique in the diagnostic laboratory? Under what circumstances might the simple stain be preferable to the Gram stain technique? 2. Suppose a student reached for the alcohol bottle for decolonization step and instead took the bottle of distilled water. What would be the color of grampositive and a gram-negative bacterium at the conclusion of the procedure? Explain thoroughly. 3. How might the Gram stain technique be of value in establishing the purity of a culture of bacteria? 4. Illustrate the result if congo red, an acidic dye, was substituted for safranin in the Gram stain technique. 5. Describe the procedures needed to properly see Gram stained organisms with the oil-immersion lens. Chapter #16 The Genus Mycobacterium 1. In what ways in the acid-fast technique similar to the gram stain technique? How does it differ? 2. If the cells from mixed smear were observed after each step of the acid-fast or cold acid-fast procedure, predict the colors of the cells at each step. 3. Why are the acid-fast procedures considered differential staining techniques? 4. Suppose alcohol instead of acid-alcohol were used in the acid-fast technique. Would decolonization take place? How would this affect the results? 5. Explain the diagnostic importance of the acid-fast technique. Chapter #5 The negative stain technique 1. Explain why crystal violet, a basic stain, would not be useful in the negative stain technique. 2. What are the advantages of 1) the negative stain technique over the simple stain technique and 2) the simple stain technique over the negative stain technique ? 3. Suppose a clean slide was used for this exercise and still a number of unexpected bacteria appeared in the finished smear. What might be their source? 4. Why is it a poor idea to heat-fix bacterial smears when performing the negative stain technique? 5. Compare the size of an organism observed after negative staining with the size of the same organism stained by the simple stain technique. Explain the reasons for any differences. Chapter #4 Preparation of a bacterial smear and the simple stain technique 1. Identify the steps taken in the preparation of a bacterial smear to prevent contamination of the culture and the preparer of the smear. 2. Summarize the fundamental theory of simple staining. 3. Judge the result of placing a large drop of water on the slide instead of loopful. 4. Discuss the possible outcomes if an air-dried smear were not heat-fixed before proceeding with the staining step. 5. When you observe your stained smear at 1000X, you see two different shaped bacteria; some are rod shaped while others are bacterial. Explain this result considering the original source culture was pure. Chapter #3 The compound microscope 1. Explain the problem encountered when magnifying an object with the oil immersion lens and indicate how immersion oil helps solve the problem. 2. Why do you use only the fine adjustment knob when viewing specimens with the high power (40x) objective and with the oil-immersion (100x) objective? 3. Describe the important steps that should be taken to care for the microscope during and after use in the laboratory. 4. What does the adjective (parfocal) mean when applied to a microscope? How is it a valuable asset in the use of the microscope? 5. Explain resolving power and working distance as they apply to the microscope. Determine the resolving power of your microscopes, using the oil immersion objective. Can a spherical bacterium measuring (3Um) in diameter be seen with the oil immersion lens? Explain • The resolving power (RP)= A (wavelength of light) -------------------------------2 NA (numerical aperture) Assume A= 500 nm and NA=1.25
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Running head: MICROBIOLOGY LAB QUESTIONS

Microbiology Lab Questions
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MICROBIOLOGY LAB QUESTIONS

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Microbiology Lab Questions
A. Bacterial culture characteristics
1. After the incubation period, why is it best to refrigerate culture plates and tubes rather
than storing them at room temperature?
The greater the cell density, the better the recovery is after thawing the cells. However
freezing at an appropriate rate helps in minimizing damage from the freezing process.
2. How can you account for the observation that a mass or colony of bacteria shows
pigmentation while the individual cells have transparent cytoplasm?
Certain Some bacteria express only some types of proteins when the color is enough for a
colony bacterium often thousands or millions to indicate a pronounced color (Buller,
2014).
3. Describe the factors that may alter the expression of the cultural characteristics of
bacteria?
Temperature and density are the fundamental factors that influence the physical
characteristics of bacteria. Density leads to coloring and temperature affects the life of
such bacteria.
4. Determine which cultural characteristics noted in this exercise are more distinctive than
others.
Temperature as a cultural characteristic is more distinctive than others since it influences
the life of the particular bacteria. Very low or very high temperatures may be dangerous
to bacteria.
5. Suppose your unknown prefers to grow at 75C, yet both slants show similar growth.
Provide some reasons to account for this observation.

MICROBIOLOGY LAB QUESTIONS

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Other than temperature, density is also a fundamental factor that influences the growth of
bacteria. Therefore, density would have been the case in this particular instance.
B. Bacterial Structural Characteristics
1. Describe several instances, other than those in the introduction to this exercise, where
identification of a bacterial unknown is bacterial and necessary.
When the color of bacteria is different from a known colony, then it is necessary to use s
bacterial means of determining the kind of bacteria in question.
2. Which structural characteristics in this exercise were most helpful in narrowing the
identification of the unknown bacterium? Which tests were least helpful? Why?
The cytoplasm in this exercise was the major structural factor in bacteria that was used to
determine and differentiate bacteria from one another (Barocchi, & Telford, 2014).
3. Before doing the spore stain, what information from the Gram stain results may assist
you in a preliminary determination for the presence of spores?
Before making a stain to determine the spores present in a bacteria. It is important to
examine the mois...


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