Chapter 6: Microbial Growth Flashcards
What is the optimal temperature range of psychrophiles?
-10C to 20C with an optimum 15*C
What is the optimal temperature range of psychrotrophs?
0 to 30C with an optimum at 24C **These can grow in the fridge.
What is the optimal temperature range of Mesophiles?
10C to 48C with an optimum at 37*C
What is the optimal temperature range of Thermophiles?
40C to 72C with an optimum an optimum at 63*C
What is the optimal temperature range of hyperthermophiles?
65C to 110C with an optimum at 92*C
Obligate Aerobes (TOP OF THE TEST TUBE OF AGAR)
The presence of enzymes allow toxic forms of oxygen to be neutralized.
Facultative Anaerobes (LOCATED JUST UNDER OBLIGATE AEROBES, BUT SPREAD THROUGHOUT TUBE)
Prefer to be aerobic, but can use fermentation or anaerobic respiration when oxygen is unavailable.
Obligate Anaerobes (BOTTOM OF THE TEST TUBE)
Lack the enzymes to neutralize oxygen; end up producing peroxide as a bi product that is actually toxic to them.
Aerotolerant Anaerobes (LOCATED THROUGHOUT THE TEST TUBE)
Have the enzymes to neutralize oxygen, but do not use it for growth. They ferment carbohydrates to lactic acid, and are used in producing pickles and cheese.
Microaerophiles (CONCENTRATED CENTRALLY IN THE TEST TUBE)
REQUIRE oxygen, but can only handle it in small concentrations.
What are the 4 phases of microbial growth?
- Lag; 2. Log; 3. Stationary; 4. Death
What is happening during the Lag phase?
Intense activity, preparing for growth, but no population increase yet.
What is happening during the Log phase?
Log or exponential increase in population
What is happening during the stationary phase?
Period of equilibrium; microbial deaths and a balance of production of new cells.
What is happening during the death phase?
The population is DECREASING at a logarithmic rate. Death exceeds new growth.
What are the direct methods of measuring microbial growth?
Plate count, direct microscope count, filtration, most probable number method
Plate count
Counting number of viable cells; disadvantage is that it has to be incubated overnight.
Direct microscope count
Advantage: quick and easy. Disadvantages include: motile bacteria are difficult to count, dead cells are counted too, a high concentration of cells is required to actually be countable
Filtration
bacteria are retained on the surface of a membrane filter and then transferred to a culture medium to grow and subsequently be counted
Most probable number method
Advantage: useful for microbes that will not grow on solid media. Disadvantage: the MPN is a statement that there is a 95% chance the bacterial population falls within a certain range.
What are the indirect methods used for measuring microbial growth?
Turbidity, metabolic activity, dry weight
Turbidity
Shows growth pattern, but does not give exact number of organisms
Metabolic activity
The amount of certain metabolic PRODUCT in direct proportion to the number of bacteria present. (ex. acid production is used to determine the amount of vitamins)
