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- Moderate-temperature-loving microbes
- Opt. temp = 25-40˚C
- most common type
- many pathogenic bacteria = 37˚C opt. temp
- Heat-loving microbes
- Opt. temp = 50-60˚C
- cannot grow below 45˚C
- not considered a public health problem
Optimum growth temperature
the temperature at which the species grows best.
- 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)
- 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
- Opt. temp = 80˚C or higher
- live in hot springs
What is the pH level most bacteria grow the best?
- 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.
torelant of acidity
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
Shrinkage of the cell's cytoplasm, which inhibit bacterial growth
- 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
- 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
- Both aerobic and anaerobic growth; greater growth in presence of O2Growth is best where most O2 is present,but occurs throughout tube
- Grows the most at the top of the tube and throughout the tube
- Only anaerobic growth; ceases in presence of O2Growth occurs only where there is no O2Grows at the bottom of the tube
- Only anaerobic growth; but continues in presence of O2Growth occurs evenly; O2 has no effect
- Grows all over the tube
- 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 O2Grows at the middle of the tube