Chapter 5: Control of Microbial Growth - Filtration, Temp, Pressure, etc.

Question 1

What is filtration? (2)

Answer 1

• vacuum used to force liquid through a filter with very small pores
• pores are too small for bacteria to pass

Question 2

What are the sizes of the pores used in filtration?

Answer 2

• 0.1 μm, 0.22 μm or 0.45 μm

Question 3

What type of liquids is filtration used to sterilize? Give some examples (4)

Answer 3

• temperature sensitive liquids
• antibiotics
• enzymes
• some vaccines

Question 4

What filters are used in Air filtration?

Answer 4

• High-efficiency particulate air (HEPA) filters

Question 5

Why do operating rooms use air filtration?

Answer 5

• to remove all microbes larger than 0.3 μm

Question 6

What are two low temperature ways to control microbial growth?

Answer 6

• refrigeration and freezing

Question 7

What does refrigeration do to microbes?

Answer 7

• slows or stops microbial growth
• bacteriostatic (or germistatic)

Question 8

What does freezing do to microbes? (3)

Answer 8

• stops microbial growth
• only a small portion of microbes die
• bacteriostatic

Question 9

What does high pressure do to microbes in liquid suspensions? (2)

Answer 9

• may kill bacterial cells (bactericidal)
• does not kill endospores

Question 10

High pressure ___ is/is not sterilization.

Answer 10

is not

Question 11

What is desiccation?

Answer 11

• removal of water (drying)

Question 12

Does desiccation kill microbes? (3)

Answer 12

• slows or stops growth
• usually does not kill microbes
• bacteriostatic

Question 13

What is osmotic pressure? (2)

Answer 13

• high concentrations of salts and sugars
• hypertonic environment

Question 14

Does osmotic pressure kill microbes? (3)

Answer 14

• can kill some bacteria
• can be bactericidal or bacteriostatic
• molds and yeasts are more resistant

Question 15

What microbes does radiation kill?

Answer 15

• DNA
• you would usually use radiation after the other techniques to kill DNA

Question 16

What occurs in radiation? (2)

Answer 16

• X-rays and Gamma rays penetrate materials
• UV and high energy electron beams used on surfaces

Question 17

How are microwaves used to kill microorganisms? (3)

Answer 17

• do not kill microorganisms directly
• they heat water
• then high temps can be used to disinfect materials

Question 18

In lecture, why does heating a towel to sterilize it not work?

Answer 18

• some ppl wet a kitchen towel and put it in the microwave to remove smell
• not effective since water must be heated FIRST before the microwave can kill the microbes