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2011-11-13 16:30:52

Chapter 7
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  1. 1.) Which of the following does not kill endospores?

    A) autoclaving
    B) hot-air sterilization
    C) pasteurization
    D) incineration
    E) all of the above kill endospores
    C) pasteurization
    (this multiple choice question has been scrambled)
  2. 2.) Which of the following is most effective for sterilizing mattresses and plastic Petri dishes?

    A.) chlorine
    B.) nonionizing radiation
    C.) glutaraldehyde
    D.) autoclaving
    E.) ethylene oxide
    E.) ethylene oxide
    (this multiple choice question has been scrambled)
  3. 3.) Which of these disinfectants does not act by disrupting the plasma membrane?

    A.) halogens
    B.) biguannides
    C.) phenolics
    D.) phenol
    E.) quaternary ammonium compunds
    A.) halogens
    (this multiple choice question has been scrambled)
  4. 4.) Which of the following cannot be used to sterilize a heat-labile solution stored in a plastic container?

    A.) gamma radiation
    B.) ethylene oxide
    C.) nonionizing radiation
    D.) short-wavelength radiation
    E.) autoclaving
    E.) autoclaving
    (this multiple choice question has been scrambled)
  5. 5.) Which of the following is not a characteristic of quarternary ammonium compounds?

    A.) sporicidal
    B.) fungicidal
    C.) bactericidal against gram-posotive bacteria
    D.) kills enveloped viruses
    E.) amoebicidal
    A.) sporicidal
    (this multiple choice question has been scrambled)
  6. 6.) A classmates is trying to determine how a disinfectant might kill cells. You observed that when he spilled the disinfectant in your reduced litmus milk, the litmus turned blue again. You suggest to your classmate that

    A.) the disinfectant might oxidixe molecules
    B.) the disinfectant might denature proteins
    C.) he take his work away from yours
    D.) the disinfectant might inhibit cell wall synthesis
    E.) the disinfectant might inhibit protein synthesis
    A.) the disinfectant might oxidixe molecules
    (this multiple choice question has been scrambled)
  7. 7.) Which of the following is the most likely to be bactericidal?

    A.) membrane filtration
    B.) ionizing radiation
    C.) deep-freezing
    D.) lyophilization (freez-drying)
    E.) all of the above
    B.) ionizing radiation
    (this multiple choice question has been scrambled)
  8. 8.) Which of the following is used to control microbial growth in foods?

    A.) aldehydes
    B.) organic acids
    C.) alcohols
    D.) heavy metals
    E.) all of the above
    B.) organic acids
    (this multiple choice question has been scrambled)
  9. 9.) Which disinfectant is the most effective?
    • A.) 1:2 NG
    • 1:4 NG
    • 1:8 NG
    • 1:16 G
  10. 10.) Which disinfectant(s) is (are) bactericidal?
    B.) A, C, and D
  11. The thermal death time for a suspension of Bacillus subtilis endospores is 30 minutes in dry heat and less than 10 minutes in an autoclave. Which type of heat is more effective? Why?
    Autoclave. Because of the high specific heat of water, moist heat is readily transferred to cells.
  12. If pasteurization does not achieve sterilization, why is pasteurization used to treat food?
    Pasteurization destroys most organisms that cause disease or rapid spoilage of food.
  13. Thermal death point is not considered an accurate measure of the effectiveness of heat sterilization. List three factors than can alter thermal death point.
    • Variables that affect determination of the thermal death point are:
    • The innate heat resistance of the strain of bacteria.
    • The past history of the culture, whether it was freeze-dried, wetted, etc.
    • The clumping of the cells during the test.
    • The amount of water present.
    • The organic matter present.
    • Media and incubation temperature used to determine viability of the culture after heating.
  14. The antimicrobial effect of gamma radiation is due to (a)_____. The antimicrobial effect of ultraviolet radiation is due to (b)_____.
    • (a.) the ability of ionizing radiation to break DNA directly. However, because of the high water content of the cells, free radicalS (H and OH) that break DNA strands are likely to form.
    • (b) formation of thymine dimers.
  15. How do autoclaving, hot air, and pasteurization illustrate the concept of equivalent treatment?
    All three processes kill microorganisms; however, as moisture and/or temperatures are increased, less time is required to achieve the same result.
  16. How do salts and sugars preserve foods? Why are these considered physical rather than chemical methods of microbial control? Name one food that is preserved with sugar and one preserved with salt. How do you account for the occasional growth of Penicillium mold in jelly, which is 50% sucrose?
    Salts and sugars create a hypertonic environment. Salts and sugars (as preservatives) do not directly affect cell structures or matabolism; instead, they alter the osmotic pressure. Jams and jelly are preserved with sugar; meats are usually preserved with salt. Molds are more capable of growth in high osmotic pressure than are bacteria.
  17. The use of dilution values for two disinfectants tested under the same conditions are as follows: Disinfectant A-1:2; Disinfectant B-1:10,000. If both disinfectants are designed for the same purpose, which would you select?
    Disinfectant B is preferable because it can be diluted more and still be effective.
  18. A large hospital washes burn patients in a stainless steal tub. After each patient, the tub is cleaned with a quat. It was noticed that 14 of 20 burn patients acquired Pseudomonas infections after being bathed. Provide an explanation for this high rate of infection.
    Quaternary ammonium compounds are most effective against gram-positive bacteria. Gram-negative bacteria that were stuck in cracks or around the drain of the tub would not have been washed away when the tub was cleaned. These gram-negative bacteria could survive the washing procedure. Some pseudomonads can grow on quats that have been accumulated.