Chapter 4: Microbial Growth - Influence of Environmental Factors (temp)

Question 1

What are environmental factors that affect microbial growth? (4)

Answer 1

• temperature
• oxygen
• pH
• osmotic pressure

Question 2

Why does temperature affect microbial growth?

Answer 2

• each species of microbe has its own specific temperature range
• this range usually spans about 30°C

Question 3

Describe the following temperature ranges:
1) minimum
2) optimal
3) maximum

Answer 3

1) lowest temperature supporting growth
2) temperature that supports best growth (usually 37°C)
3) highest temperature supporting growth

Question 4

Describe the following temperature ranges:
1) minimum
2) optimal
3) maximum

Answer 4

1) lowest temperature supporting growth
2) temperature that supports best growth (usually 37°C)
3) highest temperature supporting growth

Question 5

Bacteria can be grouped based on temperature range. List the different groups. (5)

Answer 5

• psychrophiles
• psychrotrophs
• mesophiles
• thermophiles
• hyperthermophiles

Question 6

What is the temperature range of psychrophiles? (3)

Answer 6

• cold loving
• grow between -5°C to about 15°C
• killed at 20°C

Question 7

What is the temperature range of psychrotrophs?

Answer 7

• have a very broad temperature range
• min is about -5°C
• max is about 30-45°C
  -optimum is 15-30°C

Question 8

What type of microbes are psychrotrophs?

Answer 8

• these are the microbes that cause food to spoil in the fridge

Question 9

What is the temperature range of mesophiles? (4)

Answer 9

• moderate temperature loving
• min is about 10°C
• max is about 45°C
• optimum is 24-45°C

Question 10

Which category of bacteria based on temperature range are mostly occupied by bacteria? (2)

Answer 10

mesophiles
- most pathogens (disease causing microbes) have temp optimum of 37°C

Question 11

What is the temperature range of thermophiles? (4)

Answer 11

• heat loving
• min is about 40°C
• max is about 80°C
• optimum is about 65°C
  note that thermophiles help in PCR (Taq)

Question 12

What is the temperature range of hyperthermophiles?

Answer 12

• min is about 75°C
• max is up to 121°C
• restricted to very few places on Earth where water reaches these temperatures
  ex. deep ocean vents

Question 13

Why is temperature important in microbial growth of foods?

Answer 13

• food safety involves the use of both hot and cold temperatures

Question 14

How does heat play a role in food safety?

Answer 14

• heat is used to kill mesophilic and psychrotrophic microbes (cooking)

Question 15

How does cold temperature play a role in food safety? (2)

Answer 15

• cold temp is used to slow growth
• only psychrotrophs will grow in a refrigerator, and very slowly