Microbio Ch.6 Microbial Growth

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Microbio Ch.6 Microbial Growth
2011-10-05 16:13:55
Microbial Growth

Midterm II
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  1. Phychrophiles
    Cold-loving microbes
  2. Mesophiles
    • Moderate-temperature-loving microbes
    • Opt. temp = 25-40˚C
    • most common type
    • many pathogenic bacteria = 37˚C opt. temp
  3. Thermophiles
    • Heat-loving microbes
    • Opt. temp = 50-60˚C
    • cannot grow below 45˚C
    • not considered a public health problem
  4. Optimum growth temperature
    the temperature at which the species grows best.
  5. Psychrophiles
    • can grow at 0˚C but has an optimum growth temp of about 15˚C
    • most of these organisms are so sensitive to higher temp that they will not even grow in a reasonably warm room (25˚C)
  6. Psychrotrophs
    • can grow at 0˚C
    • has higher optimum temp, usually 20-30˚C
    • cannot grow above about 40˚C
    • cause low-temp food spoilage = make spoilage in the refrage
  7. Hyperthermophiles
    • Opt. temp = 80˚C or higher
    • live in hot springs
  8. What is the pH level most bacteria grow the best?
    • pH6.5-7.5
    • very few bacteria can grow at below pH4.
    • That's why number of foods, such as sauerkraut, pickles, and many cheeses, are preserved from spoilage by acids produced by bacterial fermentation.
  9. Acidophiles
    torelant of acidity
  10. High osmotic pressure
    when a microbial cell is in a solution whose concentration of solutes is higher than in the cell = the environment is hypertonic to the cell
  11. Plasmolysis
    Shrinkage of the cell's cytoplasm, which inhibit bacterial growth
  12. Food preservation
    • pH: create lower pH (Acidic) using acids produced by bacterial fermentation because most of the bacteria cannot grow below pH4.
    • ex) sauerkraut, pickles, cheese

    • Osmotic pressure: Create hypertonic environment for the cell using salts or sugers so that it causes plasmolysis (shrinkage of the cell) and the bacteria cannot grow.
    • ex) salted fish, honey, sweetened condensed milk
  13. Obligate Aerobes
    • Only aerobic growth = O2 required
    • Growth occurs only where high concentration of O2 have diffused into the medium
    • Grows on top of the tube of Solid Growth Medium
  14. Facultative Anaerobes
    • Both aerobic and anaerobic growth; greater growth in presence of O2
    • Growth is best where most O2 is present,but occurs throughout tube
    • Grows the most at the top of the tube and throughout the tube
  15. Obligate Anaerobes
    • Only anaerobic growth; ceases in presence of O2
    • Growth occurs only where there is no O2
    • Grows at the bottom of the tube
  16. Aerotolerant Anaerobes
    • Only anaerobic growth; but continues in presence of O2
    • Growth occurs evenly; O2 has no effect
    • Grows all over the tube
  17. Microaerophiles
    • Only aerobic growth; O2 required in low concentration
    • Growth occurs only where a low concentration of O2 has diffused into medium
    • Produce lethal amounts of toxic forms of O2 if exposed to normal atmospheric O2
    • Grows at the middle of the tube