Micro Test 2

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Micro Test 2
2013-03-06 19:20:18
Bacterial Growth Culturing

Bacterial Growth and Culturing
Show Answers:

  1. At what pH range do you find extreme acidophiles and extreme alkophiles?
    Extreme Acidophiles: 0-2 and Extreme Alkophiles: 12-14
  2. At what pH range do most fungi and bacteria grow?
    Bacteria: 6.5 to 7.5 (neutral) and Fungi: 4.5-6 (slightly acidic optimums
  3. Why are honey, jam, smoked fish, and beef jerky typically microbe free?
    Because they are in solutes (sugar and salt) and inhibit mircrobial growth.
  4. What is the difference between extreme, obligate, and facultative halophiles?
    Extreme or obligate halophiles require high salt concentrations and facultatvie halophiles do not require but may grow in higher salt concentrations.
  5. What is a root nodule?
    Extra lobes in the roots of certain plants in which bacteria stay.
  6. Which process produces more energy, aerobic or anaerobic respiration?
    Aerobic respiration
  7. What is agar?
    complex polysaccharide derived from algae that serves as a thickener to make media. Cannot be digested by most microbes and melts at the same temperature as boiling water, solidifies at 40 degrees C.
  8. What is chemically defined media?
    media in which the exact chemical composition is knows.
  9. What is complex media?
    energy, carbon, nitrogen, sulfur are all from protein (extracts from yeast, meats and plants, peptone broth (nutrient broth), peptone agar (nutrient agar)
  10. What is selective media?
    suppress the growth of all but the selected microbes (media with a pH of 5.6 for fungal growth)
  11. What is differential media?
    make identification of a particular microbe from surrounding colonies possible or it can be used to classify organisms based on how they react with the media.
  12. What is enrichment media?
    designed to increase the numbers of a particular bacterium over those of others in a mixed culture. May involve a series of transfers to media containing nutrients that only the selected bacteria can metabolize.
  13. What type of bacteria do you culture on reducing media?
    Anaerobic, it contains ingredients that combine with oxygen to deplete it from the culture.
  14. What method is used to obtain pure culture from a mixed culture?
    Streak plating is a method for isolating colonies, cells from separate colonies may then be transferred to separate plates.
  15. How do bacteria divide?
    binary fission (cell elongates and DNA replicates, cell wall and membrane grow inward until they meet and the cell separates)
  16. What is generation time?
    time required for population to double. Varies by species and environmental conditions
  17. There are 4 growth phases, define lag phase?
    the number of cells changes very little initially. May last 1 hour or several days as bacteria adapt
  18. There are 4 growth phases, define exponential growth phase (log phase)
    number of bacteria doubles at a regular interval. Cells are metabolically active and sesitive to antimicrobial drugs and other deterrents
  19. There are 4 growth phases, define stationary phase
    number of deaths equals number of divisions and population stabalizes. Metabolic activity slows and food source becomes depleted and waste products build up which may alter pH of the medium
  20. There are 4 growth phases, define decline or death phase
    cells die at higher rate than division occurs. Population may die off completely or a few cells may remain
  21. Define plate counts
    measure number of viable (living cells). The original inoculum is diluted several times by serial dilution so that the number of colonies is reduced to a countable number.
  22. Define filtration
    good for solutions containing small bacterial populations (stream and lake water). Sample passed through filter with pores small enough to capture bacteria.
  23. Define direct microscopic count
    bacterial solution is dropped onto a cell counter slide. Number present is determined under high power on microscope and multiplies by a calibration factor to determine bacterial concentration in the solution. Not good for moving bacteria, no way to distinguish live from dead.
  24. What is the turbidity method of determining bacterial counts?
    when bacteria grows the solution becomes cloudy. Spectophotometer measure the amount of light transmitted through solution to give optical density measurement (OD). Both live and dead counted, small concentrations may not be detected.
  25. What is sterilization?
    removal of all microbial life
  26. What is commercial sterilzation?
    killing botulism (C. botulinum endospores)
  27. What is disinfecton?
    removal of pathogens
  28. What is antisepsis?
    removal of pathogens from living tissue
  29. What is degerming?
    removal of microbes from a limited area
  30. What is sanitization?
    lower microbial counts on for example eating utensils.
  31. What is aseptic?
    maintenance of conditions what significantly reduce risk of infection by pathogens