Chapter 5: Control of Microbial Growth - Heat + Dry Heat

Question 1

How does heat kill microbes? (2)

Answer 1

• destroys enzymes
• bactericidal (germicidal)

Question 2

What are several heat techniques to kill microbes? (3)

Answer 2

• boiling
• pasteurization
• Autoclave

Question 3

Boling for 5 minutes can kill what microbes?

Answer 3

• most pathogenic bacteria
• most viruses

Question 4

Boiling for 5 minutes cannot kill all ____.

Answer 4

endospores

Question 5

Is boiling disinfection or sterilization?

Answer 5

• disinfection

Question 6

What is pasteurization?

Answer 6

• sufficient to eliminate pathogens and to lower microbial numbers to slow spoilage

Question 7

What temperatures is used for these types of pasteurization?
a) classic treatment
b) HTST (high temp short time)
c) UHT (ultra high temp)

Answer 7

a) 63°C for 30 minutes
b) 72°C for 15 seconds
c) 140°C for 3 seconds

Question 8

What type of microbes does UHT kill?

Answer 8

all microorganisms that can grow under normal storage conditions

Question 9

What does an autoclave do?

Answer 9

• employs pressure (15 psi) and steam (121°C)

Question 10

What type of microbes does an autoclave kill?

Answer 10

• all endospores in about 15 minutes

Question 11

The autoclave is the best method of ____

Answer 11

sterilization

Question 12

What is an autoclave used for? (2)

Answer 12

• culture media
• hospital instruments b/c hospital materials can withstand heat and moisture

Question 13

If you are using an autoclave, what must you ensure? (3)

Answer 13

• all solid surfaces are exposed to steam
• all liquids must reach 121°C
• usually cover the glass in porous material

Question 14

In lecture, does using an autoclave kill DNA? Why?

Answer 14

• no
• lets say you wanna decontaminate a flask containing bacteria in liquid
• the DNA can survive by sticking to the porous material

Question 15

What are 3 methods of dry heat sterilization?

Answer 15

1. direct flaming
2. Incineration
3. Hot air sterilization

Question 16

What is direct flaming?

Answer 16

• used in labs to sterilize inoculation needles and loops

Question 17

In lecture, why do we do direct flaming? (2)

Answer 17

• to pick a tiny colony and transfer to new broth
• but we need to wait 30 sec after heating or else we might kill the colony with heat!

Question 18

What is incineration?

Answer 18

• effective way to dispose of contaminated materials

Question 19

What is hot air sterilization?

Answer 19

• drying oven used for dry materials that are not temperature sensitive

Question 20

What temperature should materials undergoing hot air sterilization be at?

Answer 20

• 170°C for 2 hours