Chapter 5 Control of Microbial Growth

Question 1

Sterilization

Answer 1

Absolute removal or destruction of ALL microorganisms and viruses

Question 2

Disinfection

Answer 2

• Destruction of most microbes including pathogens
• Does not kill all microbes
• Ex. Chemical disinfectants

Question 3

Antisepsis (Antiseptic)

Answer 3

• Disinfection of skin or living tissue

- Normally using less harsh treatments (chemicals)

Question 4

Degerming

Answer 4

• Removal of MOST microbes from a limited area

- Ex. Washing hands with soap and water

Question 5

Sanitization

Answer 5

Lowering microbial counts to a safe level to meet public health standards

Question 6

-cidal vs. -static

Answer 6

-An agent that kills microbes has the suffix -cide
- An agent that stops the growth of microbes -static or -stasis
Example:
1) A bacteriocidal kills bacteria
2) A bacteriostatic agent stops bacteria from reproducing

Question 7

Asepsis (aseptic)

Answer 7

• An area is free of significant contamination

- Modern surgical techniques are aseptic to minimize infection

Question 8

Using Heat to Destroy Microbes

Answer 8

• Kills microbes by destroying enzymes - bactericidal (germicidal)
• Can be used several ways:
  1) Boiling for 5 minutes
  2) Pasteurization
  3) UHT
  4) Autoclave

Question 9

Boiling for 5 minutes

Answer 9

• Kills most pathogenic bacteria- but not all endospores
• Most Viruses
• This is disinfection, not sterilization!

Question 10

Pasteurization

Answer 10

• Sufficient to eliminate pathogens and to lower microbial numbers to slow spoilage
• Classic treatment = mild heating to 63 degree C for 30 minutes
• HTST (High Temperature Short Time) = 72 degree C for 15 seconds

Question 11

UHT (Ultra High Temperature)

Answer 11

• =140 degree C for 3 seconds

- Destroys all microorganisms that can grow under normal storage conditions

Question 12

Autoclave

Answer 12

• Employs pressure (15 psi) and steam (121 C)
• Kills all endospores in about 15 mins
• Best method for sterilization
• Used for:
  1) Culture Media 2) Hospital instruments 3) Hospital materials that can withstand heat and moisture
  4) Requires that all solid surfaces are exposed to steam
  5) All liquids must reach a temperature of 121 C

Question 13

Dry Heat Sterilization (methods)

Answer 13

• Direct Flaming
• Incineration
• Hot air sterilization

Question 14

Direct Flaming

Answer 14

• Dry heat sterilization
• Used in microbiology laboratory to sterilize inoculation needles and loops
• Metallic instruments must be red-hot

Question 15

Incineration

Answer 15

Effective way to dispose of contaminated materials

Question 16

Hot Air Sterilization

Answer 16

• Drying oven
• Materials should stay at 170C for 2 hours
• Used for dry materials that are not temperature sensitive
• Examples: Glassware, some dry chemicals

Question 17

Filtration

Answer 17

-Vacuum used to force liquid through filter with very small pores - 0.1um, 0.22um or 0.45um
-Pores are too small for bacteria to pass
-Used to sterilize temperature sensitive liquids:
Antibiotics
Enzymes
Some vaccines

Question 18

Air Filtration

Answer 18

• High-efficiency particulate air (HEPA) filters

- Used in some operating room to remove all microbes larger than 0.3um

Question 19

Refrigeration and Freezing (Low Temperatures)

Answer 19

Refrigeration

• Slows or stops microbial growth
• Bacteriostatic (or germistatic)

Freezing

• Stops microbial growth
• Only a small portion of microbes will die
• Bacteriostatic

Question 20

High Pressure

Answer 20

• Liquid suspensions treated with high pressure
• May kill many bacterial cells- bacteriocidal
• Does not kill endospores
• Not sterilization

Question 21

Dessication

Answer 21

• Removal of water (drying)

- slows or stops growth - but usually does not kill microbes - bacteriostatic

Question 22

Osmotic Pressure

Answer 22

• High concentrations of salts and sugars - hypertonic environment
• Can kill some bacteria - bacteriocidal or bacteriostatic
• Molds and yeasts are more resistant

Question 23

Radiation

Answer 23

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

Question 24

Microwaves

Answer 24

• Do not kill microorganisms directly
• They heat water
• High temperatures can be used to disinfect materials

Question 25

Chemical used to Destroy Microbes

Answer 25

-Most can only be used for disinfection - not sterilization

Question 26

Disk Diffusion Method

Answer 26

- Disk of filter paper soaked in chemical disinfectant - Placed on ager plate that has already been inoculated with bacteria - The plate is incubated until bacteria grow - Zone of clearing determines effectiveness

Question 27

Phenolic Compound (Phenols)

Answer 27

- Disrupt plasma membranes, denature proteins - Bacteriocidal - Very effective, remain active long after application - Suitable for disinfection of soiled surfaces - Often mixed with other compounds to reduce toxicity

Question 28

Hexachlorophene (Phenols)

Answer 28

- Useful against bacteria that cause skin infections in newborns - Can be used to disinfect surfaces in nurseries - Caution must be used - causes neurological disorders

Question 29

Triclosan (Phenosl)

Answer 29

Used in some personal hygiene products - cosmetics and deodorant soaps

Question 30

Biguanides

Answer 30

1) Chlorhexidine - attacks membrane (bacteriocidal) - To control microbes on skin and mucous membranes 2) Used in surgical hand scrubs - Can persist for up to 6 hours - Only kills some viruses, does not destroy endospores

Question 31

Halogens

Answer 31

- Destroys proteins and membranes - Used as disinfectants and antiseptics: 1) Chlorine 2) Iodine

Question 32

Chlorine

Answer 32

- Forms hypochlorous acid in water - strong oxidizing agent - denatures enzymes - Examples: 1) Household bleach (sodium hypochlorite) --> excellent disinfectant 2) Chlorine dioxide - sterilizing gas

Question 33

Iodine

Answer 33

- Frequently used as an antiseptic - Examples: 1) Tincture of iodine - in an alcohol solution 2) Iodophore - linked to carrier molecules so that is released slowly over time (Betadine)

Question 34

Alcohols

Answer 34

- Denature proteins and disrupt membranes - Kills bacteria and fungi - Does not kill endospores and some viruses - Often used to disinfect surfaces in a lab, or to degree skin - Does not suffice as an antiseptic (combined with other chemicals to enhance)

Question 35

Ethanol (Type of Alcohol)

Answer 35

70% most effective

Question 36

Isopropanol

Answer 36

Rubbing alcohol

Question 37

Silver Nitrate (Heavy Metal)

Answer 37

- 1% | - Used as eye drops for new-born infants, to protect against gonorrhoeal ophthalmia

Question 38

Silver Sulfadiazine

Answer 38

Topical cream for burns

Question 39

Silver ions

Answer 39

are incorporated into bandages and catheters to slow growth of microbes

Question 40

Copper Sulfate

Answer 40

Used to inhibit algae in reservoirs

Question 41

Mercuric Chloride

Answer 41

Used in paint to control mildew (toxic!)

Question 42

Zinc Chloride

Answer 42

Used as antiseptic mouthwashes

Question 43

Gases Chemosterilizers

Answer 43

- Chemical gasses used for sterilization - Ethylene Oxide 1) Denatures proteins - germicidal 2) Kills all microbes - including endospores and viruses 3) Requires 4 -18 hours of exposure 4) Highly penetrating - passes through plastics 5) Used to sterilize disposable hospital equipment and lab supplies

Question 44

Oxidizing Agents

Answer 44

- Oxidize and denature proteins - Useful against anaerobic organisms 1) Hydrogen peroxide - common antiseptic for wounds 2) Ozone - used with chlorine to disinfect water 3) Benzoyl peroxide - used as antiseptic on skin (Kills bacteria that causes acne)