Chapter #13: Control of Microbial Growth

Question 1

Why clean and not sterilize everything?

Answer 1

Sterilization often requires time, is labor intensive and, may
degrade the quality of the item being treated, or even have
toxic effects on users

Question 2

How can microbial load be reduced?

Answer 2

Microbial load can be reduced by washing, vacuuming and
dishwashing

Question 3

Biosafety Levels

Answer 3

-ranked by the severity of disease and ease of transmission
1. BSL-1
2. BSL-2
3. BSL-3
4. BSL-4

Question 4

BSL-1

Answer 4

-microbes are not known to cause disease in healthy hosts and pose minimal risk to workers and the environment
-low-risk microbes
-ex. Nonpathogenic strains of Escherichia coli

Question 5

BSL-2

Answer 5

-Microbes are typically indigenous and are associated with diseases of varying severity
-they pose moderate risk to workers and the environment
-ex. Staphylococcus aureus

Question 6

BSL-3

Answer 6

-microbes are indigenous or exotic and cause serious or potentially lethal diseases through respiratory transmission
-ex. Mycobacterium tuberculosis

Question 7

BSL-4

Answer 7

-microbes are dangerous and exotic, posing a high risk of aerosol-transmitted infections, which are frequently fatal without treatment or vaccines
-few labs are at this level
-high-risk microbes
-ex. Ebola and Marburg viruses

Question 8

Sterilization

Answer 8

Process by which ALL living cells, spores, and viruses are destroyed on an object

Question 9

Disinfection

Answer 9

The killing or removal of DISEASE-PRODUCING organisms from inanimate surfaces; it does not necessarily result in sterilization

Question 10

Antisepsis

Answer 10

Similar to disinfection but applies to removing pathogens from the
surface of LIVING tissues, such as skin

Question 11

Sanitation

Answer 11

Consists of reducing the microbial population to safe levels and usually involves cleaning an object as well as disinfection

Question 12

Antimicrobials fall into 2 broad classes

Answer 12

1. Cidal Agents
2. Static Agents

Question 13

Cidal Agents

Answer 13

• kill microbes
  -Bactericidal, algicidal, fungicidal, virucidal, depending on what type of microbe is killed

Question 14

Static Agents

Answer 14

• inhibit or control growth
  -Bacteriostatic, algistatic, fungistatic, virustatic, depending on what type of microbe is inhibited

Question 15

Selection of Disinfectant Criteria

Answer 15

1. Must be fast-acting in the presence of organic materials
2. Must be effective against all microorganisms without destroying tissue or acting as a toxin if ingested
3. Easily penetrate the material to be disinfected without discoloration or damage.
4. Easy to prepare and stable in the environment where it is to be used
5. Inexpensive and easy to use.
6. Not have an unpleasant odor

There is no perfect disinfectant that meets all criteria

Question 16

Several factors influence the speed at which lethal damage accumulates

Answer 16

-the initial population size (The larger the population, the longer it takes to decrease it to a specific number.)
-population composition (i.e., are spores involved?)
-agent concentration or dose for radiation
-duration of exposure
-presence of organic material (blood, feces) that can inhibit disinfectant action; organic load

Question 17

Can microbes be controlled without chemicals?

Answer 17

Physical agents are often used to kill microbes or control their growth

Question 18

Commonly used physical control measures include

Answer 18

-temperature extremes
-pressure (usually combined with temperature)
-filtration
-irradiation

Question 19

High Temperature and Pressure

Answer 19

-Moist heat is very effective at killing microbes
-Dry heat is less effective, but sometimes required
-To kill spores and thermophiles, a combination of heat
and pressure is usually required (e.g., steam autoclave)
-Standard autoclave conditions are 121°C at 15 psi
(pounds per square inch) for 20 minutes

Question 20

Heat killing

Answer 20

-Preferred sterilizing agent as long as it doesn’t damage the
materials
-Thermal death point (TDP)
-Thermal death time (TDT)
-Decimal reduction time (D value)

Question 21

Thermal death point (TDP)

Answer 21

• temperature that kills all the bacteria in a 24 hour old culture/ 10 min

Question 22

Thermal death time (TDT)

Answer 22

• Time required to kill all the bacteria in a culture at a specified temperature

Question 23

Decimal reduction time (D value)

Answer 23

length of time required to kill 90% of the organisms in a population at a specific temperature

Question 24

Pasteurization

Answer 24

The goal of pasteurization is not to sterilize, but to kill
pathogens without affecting the texture, color, or taste of
the product

Question 25

Different Time and Temperature combinations can be
used

Answer 25

-Low temperature, long time (LTLT)
-High temperature, short time (HTST)
-Ultra high temperature (UHT)

Question 26

Refrigeration, freezing

Answer 26

-excellent to preserve food and other materials - retards
microbial growth
-but does not effectively kill microorganisms
-Microorganisms can be stored in this way

Question 27

Freeze-drying

Answer 27

-many microorganisms are sensitive to drying - but, many are not
-Freeze drying is used for storing many microorganisms

Question 28

Filtration

Answer 28

-Many drugs/chemicals are sensitive to heat or other chemical sterilization methods
-These solutions can be sterilized by passing them through sterile filters with tiny pore sizes that effectively “sift” the microbes out of the fluid
-Filtration through micropore filters of 0.2 µm can remove microbial cells, but not viruses, from solutions
-To remove viruses, pore sizes of 20 nm are necessary (1 nm = 0.001 µm)

Question 29

Sonication

Answer 29

-High frequency ultrasound waves to disrupt cell structures
-The disruption is achieved due to the rapid changes in pressure within the intracellular liquid

Question 30

Irradiation

Answer 30

-Method in which objects are bombarded with high-energy electromagnetic radiation
-Foods do not become radioactive when irradiated, and any reactive molecules produced when high-energy particles are absorbed by food dissipate almost immediately
-Ultraviolet (UV) light
-Gamma rays, electron beams, X-rays

Question 31

Efficacy of a given chemical agent depends upon

Answer 31

-the presence of organic matter
-the kinds of organisms present
-Corrosiveness
-stability, odor, and surface tension

Question 32

the presence of organic matter

Answer 32

Chemicals will bind to inert organic material, lowering its effectiveness against microbes

Question 33

the kinds of organisms present

Answer 33

Ideally should be effective against a broad range of
pathogens

Question 34

Corrosiveness

Answer 34

Should not corrode the surface (nonliving or living)

Question 35

stability, odor, and surface tension

Answer 35

Should be stable upon storage, neutral or pleasant odor, low surface tension

Question 36

Commercial disinfectants are all used to reduce or eliminate microbial content from commercial products

Answer 36

-ethanol, iodine, chlorine
-surfactants (such as detergents)
-aldehydes
-Phenolics
-Heavy Metals
-Peroxygens

Question 37

ethanol, iodine, chlorine

Answer 37

highly reactive compounds that damage proteins, lipids, and DNA

Question 38

surfactants (such as detergents)

Answer 38

help in the mechanical removal of microbes from surfaces

Question 39

aldehydes

Answer 39

combine with and inactivate proteins and nucleic acids

Question 40

Phenolics

Answer 40

denature proteins and disrupt membranes

Question 41

Heavy Metals

Answer 41

bind to proteins and inhibit enzymatic activity

Question 42

Peroxygens

Answer 42

strong oxidizers, produce free radicals that damage cellular
macromolecules

Question 43

Gas Sterilization

Answer 43

-Disposable plasticware such as petri dishes, syringes, sutures, and catheters are not amenable to heat sterilization or chemical disinfection

Question 44

These types of products are best sterilized by gamma
irradiation or antimicrobial gases, such as ethylene oxide (EtO)

Answer 44

-destroys proteins by alkylation
-microbicidal/sporicidal
-rapidly penetrates packing materials, including plastic
-wraps
-highly explosive

Question 45

Bacterial resistance to disinfectants

Answer 45

-Bacteria can develop resistance to chemical disinfectants used to prevent infections
-It is difficult for bacteria to develop resistance to chemical agents that have multiple targets and can easily diffuse into a cell (example: iodine)
-Disinfectants that have multiple targets at high concentrations may only have a single target at low concentrations—a situation that can foster resistance (example: triclosan)