Unit 2: Physical Methods Study Guide

Question 1

Sterilant

Answer 1

kills 100% of microbes on non-living surfaces including endospores

Ex: ethylene oxide (EtO) or hydrogen peroxide

Question 2

Disinfectants

Answer 2

process used to kill most, but not all, microbes on non-living surfaces (<100%)

Ex: pasteurization, boiling

Question 3

Antiseptic

Answer 3

used on living tissue to reduce risk of infection or sepsis (<100% on skin)

Question 4

Cidal

Answer 4

means “to kill”

Ex: Lysol, alcohol, autoclaving, boiling

Question 5

Static

Answer 5

agents that stop or slow the growth of microbes

Ex: refrigerator, freezer, preservatives in food

Question 6

Filtration

Answer 6

• REMOVAL of microbes from liquids or gas (air filtration in a patient room, face mask)
• viruses = 0.025-0.22mu
• bacteria = 0.22-0.45mu

Question 7

Radiation - Ionizing

Answer 7

• FORMS IONS by breaking apart DNA
• X-rays and Gamma rays <1nm (breaks apart DNA resulting in charged particles)
• Not easily repaired.
• can sterilize food and plastic medical equipment

Question 8

Radiation - Non-Ionizing

Answer 8

• UV light approx. 10-400nm
• this form of energy causes dimers between adjacent Thymines in DNA which changes, or mutates, the structure of DNA snd interferes with DNA replication.
• Surface disinfection (takes longer to sterilize surfaces

Question 9

Dry heat (incineration)

Answer 9

approx. 815.6 degrees C (sterilize)

Ex: metal loop

Question 10

Dry heat (dry oven sterilization)

Answer 10

170 degrees C for 2 hours (powdery substances, glass instruments, etc.)

Question 11

Ultrasonic vibration

Answer 11

• sound waves 20-40khz, disrupts membranes on microbes
• shock waves are conducted through living cells, structures, or liquids
• removal of plaque from the surface of teeth
• is cidal

Question 12

Moist heat method: Autoclaving

Answer 12

• temperature: 121 degrees C (15 psi)
• time: 15 min
• does it effectively kill endospores?: YES

Question 13

Moist heat method: Boiling

Answer 13

• temperature: 100 degrees C
• time: approx. 10 min
• does it effectively kill endospores?: DISINFECT (endospores require >2hours)

Question 14

Moist heat method: Pasteurization

Answer 14

• temperature: holding: 63 degrees C for 30 min
  flash: 72 degrees C for 15 seconds
• does it effectively kill endospores?: NO, these disinfect food and beverage

Question 15

Explain how filtration is used to remove microbes from air and water.

Answer 15

Filters utilize pores which trap microbes (liquid and gas molecules are too small to get trapped)

Question 16

How does non-ionizing UV radiation damage microbes? What type of dimers are formed?

Answer 16

• UV light approx. 10-400nm
• this form of energy causes dimers between adjacent Thymines in DNA which changes, or mutates, the structure of DNA snd interferes with DNA replication.
• dimers block DNA polymerase (DNA replication)

Question 17

List the microorganisms from least resistant to most resistant.

Answer 17

Enveloped virus (least)
Gram +
Naked Virus
Fungi
Gram -
Acid Fast
Endospore (most)

Question 18

Factors that affect microbial control

Answer 18

1. time of exposure (endospores require more time)
2. amount of microbe (microbial load)
3. resistance of microbe to treatment (endospores have protective layers)
4. type of method being used (cidal vs static)

Question 19

Osmotic pressure

Answer 19

• mostly static
• uses high concentrations of solutes (salts and sugars)
• hypertonic environment (removal of water for preservation of food)

Question 19

Dessiccation

Answer 19

• removal of water from microbial cells
  endospores are most resistant
• viruses are generally resistant