Study Guide Flashcards
- Name a bacterial species that you have encountered in this course that can be found in each of the following environments.
- Give its cell shape (coccus, bacillus) and Gram reaction.
- Is it a lactose fermenter? (Yes, No, or Don’t Know)
After performing a serial dilution of Pseudomonas aeruginosa, you plate 0.1 ml of a 10‑5 dilution. After incubating for 24 hours at 37 C, you count 112 colonies.
- A. How many CFU per ml in the 10‑3 dilution tube?
- B. How many CFU per ml in the original culture?
- C. This species gives you an oxidase-positive reaction on a dry slide. What does that tell you about its electron transport system?
- D. Is this species a psychrophile, mesophile, or thermophile?
- E. What kind of compound does this bacterium secrete that gives it a green color when you grow it at 37oC?
If you wanted to achieve a final dilution of 5 x 10-3 in a test tube, how might you best set this up while keeping dilution tubes to a minimum and using between 1.0 ml and 0.1 ml transfer volumes?
If the gradation marks on your ocular micrometer were found equal to 1.5 μm in length and you were measuring a Gram (+) rod that was 30 marks by 12 marks:
- what are the actual dimensions of this bacterium?
- Is this a reasonable finding for any of the species we observed in our course?
Describe exactly how you would combine the use of a spectrophotometer and dilution plating to make a standard curve estimating CFUs/unit OD.
For EACH of the selective and differential media you’ve encountered, discuss the chemical reactions taking place as well as the putative identity of the bacteria producing those reactions.
Questions A-F below pertain to gram staining of a Streptococcus spp
- A. What color are the cells after the first staining step and what primary stain is used?
- B. What is the color of the cells after the application of the mordant and what is the mordant?
- C. What is the color of the cells after the application of the decolorizer and what is used to decolorize?
- D. What is the color of the cells after the second staining step and what secondary stain is used?
- E. What would be the final result if you decolorized too much?
- F. What would be the final result if you mistakenly used the secondary stain first and the primary stain second?
- G. What would be the final result if you mistakenly decolorized too long?
- H. What would be the final result if you Gram stained old cells from a plate that was stored in the refrigerator for a week?
Questions A-F below pertain to gram staining of a Klebsiella spp
- A. What color are the cells after the first staining step and what primary stain is used?
- B. What is the color of the cells after the application of the mordant and what is the mordant?
- C. What is the color of the cells after the application of the decolorizer and what is used to decolorize?
- D. What is the color of the cells after the second staining step and what secondary stain is used?
- E. What would be the final result if you decolorized too much?
- F. What would be the final result if you mistakenly used the secondary stain first and the primary stain second?
- G. What would be the final result if you mistakenly decolorized too long?
- H. What would be the final result if you Gram stained old cells from a plate that was stored in the refrigerator for a week?
- What staining technique have we used that requires the use of Maneval’s Solution?
- Is it a cationic or anionic stain?
- Is it attracted to or repelled by the surface of most cells?
What is a negative stain and what bacterial cell structure can it be used to visualize?
You have an unknown sample of cells that are rod-shaped and stains Gram positive, and appears to have small clear-looking spots in each cell.
- What might these clear spots be?
- What staining technique might you perform to verify your suspicions?
- Give an example of a complex medium that you have used in class.
- How does this kind of medium differ from a defined medium?
- Autoclaving of normal microbiological culture medium should be done for at least _____ minutes at a minimum of _____ pounds per square inch of pressure and _____ degrees Celsius.
- How do you avoid the following foibles of media-making:
- boiling over the medium in the autoclave?
- getting agar plates full of bubbles?
Why do you always add agar powder AFTER you dissolve all other ingredients, check the pH of your medium, and bring it to its total volume?
What technique could you use to sterilize a heat-labile vitamin solution?
- What technique would you use to enumerate bacterial density, yielding an answer in CFU/ml?
- What technique would you use to enumerate bacteria density, yielding an answer in cells/ml?
- Why might you get different numbers from an identical culture, when counting CFU/mL and cells/mL?
- When measuring the optical density of a bacterial culture, you must have a __________________________ in order to interpolate the OD to actual cells/mL or CFU/mL.
When measuring optical density of a bacterial culture: what wavelength would you use if the cells were suspended in:
- Luria broth (LB), which is yellow in color?
- Phosphate buffer, which is clear?
- Nutrient broth, which is light brown?
When counting CFUs on a normal sized Petri plate, you want to choose plates that have fewer than ___ colonies but more than ___ colonies.
Match the reagents in the right column with the appropriate biochemical test in the left column (indicate by using each letter only once).
