Microbio Ch.6 Microbial Growth

Cold-loving microbes

• 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

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

• 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.

torelant of acidity

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 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

• Only anaerobic growth; ceases in presence of O₂
• Growth occurs only where there is no O₂
• Grows at the bottom of the tube

• Only anaerobic growth; but continues in presence of O₂
• Growth 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 O₂
• Grows at the middle of the tube