ch. 9 microbial control mechanisms

Question 1

What is moist heat? And what does it do to microbes?

Answer 1

Moist heat is heat that involves some form of water.
- ex. steam, boiling water
- operates at lower temps and short exposure times
- as effective as dry heat
- coagulates and denatures proteins

Question 2

What are some examples of moist heat?

Answer 2

• autoclaving (steam and moist heat)
• pasteurization

Question 3

What is Dry heat? What effect does it have on microbes?

Answer 3

• dry heat is heat like fire
• dehydrates cells which removes all water, denatures proteins, and at high temps burns cells
• ex. Bunsen burner, incineration, and drying oven

Question 4

What microbes are resistant to heat?

Answer 4

endospores
- requires dry heat (temps above boiling) to kill
Vegetative cells
- varying sensitivity
- death times related to heat vary for vegetative cells
Viruses:
- very resistant to moist heat
- dry heat works best

Question 5

What as radiation? and what does it do to microbes?

Answer 5

• physical control
• energy emitted from atomic activities and dispersed ar high velocity through matter/space
• breaks up DNA
  Types:
• gamma rays
• UV
• x-rays

Question 6

What is filtration, and what does it do to microbes?

Answer 6

• method where fluid is strained through filters with openings small enough to trap microbes but let liquids pass through
• pore size can be controlled for complete sterilization
• cannot remove soluble molecules that cause disease (toxins)

Question 7

When will radiation be used?

Answer 7

used on surfaces and plastic instruments

Question 8

When will filtration be used?

Answer 8

• used for things that cannot withstand heat
  ex. Vaccines serums, blood products, drugs, IV fluids, enzymes, media
• often used in water purification
• HEPA filters in hospitals to filter air

Question 9

What is osmotic pressure control? What does it do to microbes?

Answer 9

• adding large amounts of salt or sugar to foods to create a hypertonic environment
• causes plasmolysis
• never a sterilizing technique

Question 10

What are examples of osmotic pressure control?

Answer 10

pickling, smoking, and drying foods

Question 11

What are chemical control mechanisms?

Answer 11

• usually in liquid, gaseous, or solid state
• Range from disinfectants and antiseptics to sterilants and preservatives

Question 12

What are aqueous chemical controls?

Answer 12

chemicals dissolved in pure water as the solvent

Question 13

What are Tinctures?

Answer 13

chemicals dissolved in pure alcohol or water-alcohol mixtures

Question 14

What are the important qualities of a germicide?

Answer 14

• rapid action at low concentrations (to not harm tissues)
• broad spectrum microbial action w/out being toxic to human/animal tissues
• Penetration of inanimate surfaces to sustain a cumulative or persistent action
• resistance to becoming inactivated by organic matter
• not corrosive or staining
• affordable and readily available

Question 15

What factors affect the germicidal activities of chemicals?

Answer 15

• nature of microorganisms being treated (susceptible or not)
• nature of material (can these chemicals be used on a particular material)
• degree of contamination
• time of exposure (how long does microbe need to be exposed)
• strength of chemical action of the germicide

Question 16

What is essential about the length of exposure to a germicide?

Answer 16

most compounds require adequate contact time which allows chemicals to penetrate and act on microbes
- ex. alcohol evaporates very quickly compared to other chemicals