Chapter 6: Microbial Growth

Question 1

What is the optimal temperature range of psychrophiles?

Answer 1

-10C to 20C with an optimum 15*C

Question 2

What is the optimal temperature range of psychrotrophs?

Answer 2

0 to 30C with an optimum at 24C **These can grow in the fridge.

Question 3

What is the optimal temperature range of Mesophiles?

Answer 3

10C to 48C with an optimum at 37*C

Question 4

What is the optimal temperature range of Thermophiles?

Answer 4

40C to 72C with an optimum an optimum at 63*C

Question 5

What is the optimal temperature range of hyperthermophiles?

Answer 5

65C to 110C with an optimum at 92*C

Question 6

Obligate Aerobes (TOP OF THE TEST TUBE OF AGAR)

Answer 6

The presence of enzymes allow toxic forms of oxygen to be neutralized.

Question 7

Facultative Anaerobes (LOCATED JUST UNDER OBLIGATE AEROBES, BUT SPREAD THROUGHOUT TUBE)

Answer 7

Prefer to be aerobic, but can use fermentation or anaerobic respiration when oxygen is unavailable.

Question 8

Obligate Anaerobes (BOTTOM OF THE TEST TUBE)

Answer 8

Lack the enzymes to neutralize oxygen; end up producing peroxide as a bi product that is actually toxic to them.

Question 9

Aerotolerant Anaerobes (LOCATED THROUGHOUT THE TEST TUBE)

Answer 9

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.

Question 10

Microaerophiles (CONCENTRATED CENTRALLY IN THE TEST TUBE)

Answer 10

REQUIRE oxygen, but can only handle it in small concentrations.

Question 11

What are the 4 phases of microbial growth?

Answer 11

1. Lag; 2. Log; 3. Stationary; 4. Death

Question 12

What is happening during the Lag phase?

Answer 12

Intense activity, preparing for growth, but no population increase yet.

Question 13

What is happening during the Log phase?

Answer 13

Log or exponential increase in population

Question 14

What is happening during the stationary phase?

Answer 14

Period of equilibrium; microbial deaths and a balance of production of new cells.

Question 15

What is happening during the death phase?

Answer 15

The population is DECREASING at a logarithmic rate. Death exceeds new growth.

Question 16

What are the direct methods of measuring microbial growth?

Answer 16

Plate count, direct microscope count, filtration, most probable number method

Question 17

Plate count

Answer 17

Counting number of viable cells; disadvantage is that it has to be incubated overnight.

Question 18

Direct microscope count

Answer 18

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

Question 19

Filtration

Answer 19

bacteria are retained on the surface of a membrane filter and then transferred to a culture medium to grow and subsequently be counted

Question 20

Most probable number method

Answer 20

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.

Question 21

What are the indirect methods used for measuring microbial growth?

Answer 21

Turbidity, metabolic activity, dry weight

Question 22

Turbidity

Answer 22

Shows growth pattern, but does not give exact number of organisms

Question 23

Metabolic activity

Answer 23

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)