chapter 13 - control of microbial growth

Question 1

clean (term)

Answer 1

relative term, doesn’t necessarily mean clean of everything
- microbial load can be reduced by washing, vacuuming, and dishwashing but is this clean enough

whether it is clean enough or not depends on the intended use of an object or surface

Question 2

why clean and not sterilize everything?

Answer 2

1. sterilization often requires time
2. is labor intensive
3. may degrade the quality of the item being treated
4. or even have toxic effects on users

Question 3

biosafety levels ranked by the severity of disease and ease of transmission

Answer 3

(low) BSL-1→ BSL-2 → BSL-3 → BSL-4 (high)
low-risk microbes → high-risk microbes

Question 4

BSL-1

Answer 4

biosafety level 1: low-risk microbes
- microbes are not known to cause disease in healthy hosts
- pose minimal risk to workers and the environment
e.g. nonpathogenic strains of E. coli

Question 5

BSL-2

Answer 5

biosafety level 2
- microbes are typically indigenous
- are associated with diseases of varying severity
- pose moderate risk to workers and the environment
e.g. Staphylococcus aureus

Question 6

BSL-3

Answer 6

biosafety level 3
- microbes are indigenous or exotic
- causes serious or potentially lethal diseases through respiratory transmission
e.g. Mycobacterium tuberculosis

Question 7

BSL-4

Answer 7

biosafety level 4: high-risk microbes
- microbes are dangerous and exotic
- poses a high risk of aerosol-transmitted infections, which are frequently fatal without treatment or vaccines
- few labs are at this level
e.g. Ebola and Marburg viruses

Question 8

terms used to describe antimicrobial measures

Answer 8

• sterilization
• disinfection
• antisepsis
• sanitation

Question 9

sterilization

Answer 9

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

Question 10

disinfection

Answer 10

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

Question 11

antisepsis

Answer 11

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

Question 12

sanitation

Answer 12

consists of reducing the microbial population to safe levels
- usually involves: cleaning and disinfecting an object

Question 13

antimicrobials fall into 2 broad classes…

Answer 13

1. cidal agents
2. static agents

Question 14

cidal agents

Answer 14

major class of antimicrobes
- kills microbes

bactericidal, algicidal, fungicidal, virucidal
- depending on what type of microbe is killed

Question 15

static agents

Answer 15

major class of antimicrobials
- inhibit or control growth

bacteriostatic, algistatic, fungistatic, virustatic,
- depending on what type of microbe is inhibited

Question 16

6 criteria for selection of disinfectant

Answer 16

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 17

microbial death curve

Answer 17

a logarithmic function which demonstrates the rate of microbial death
- e.g. can evaluate the degree of microbial control and to describe the progress and effectiveness of a particular protocol

Question 18

several factors influence the speed at which lethal damage accumulates

Answer 18

1. the initial population size
- the larger the population, the longer it takes to decrease it to a specific number

2. population composition
- i.e. are spores involved?

3. concentration of agent or dose for radiation

4. duration of exposure

5. presence of organic material (e.g. blood, feces)
- ones that can inhibit disinfectant action
- organic load

Question 19

can microbes be controlled without chemicals

Answer 19

yes, physical agents are often used to kill microbes
- or control their growth

Question 20

commonly used physical control measures include…

Answer 20

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

Question 21

high temperature and pressure ways of killing microbes

Answer 21

• moist heat
• dry heat

Question 22

killing microbes: moist heat

Answer 22

uses water, high temperature and pressure to kill microbes
- very effective at killing microbes

steam autoclave is a type of moist heat method

Question 23

killing microbes: dry heat

Answer 23

uses only high temperature and pressure to kill microbes
- requires higher temperatures than moist heat
- less effective than moist heat but is sometimes required

Question 24

steam autoclave

Answer 24

form of moist heat to kill microbes
- to kill spores and thermophiles, a combination of heat and pressure is usually required

standard autoclave conditions
- 121 degrees C
- 15 psi (pounds per square inch)
- 20 minutes

Question 25

heat killing

Answer 25

**preferred sterilizing agent** - as long as it doesn't damage the materials **associated terms:** - thermal death point (TDP) - thermal death time (TDT) - decimal reduction time (D value)

Question 26

thermal death point (TDP)

Answer 26

**temperature that kills all the bacteria in a 24 hour old culture in 10 min of exposure** - in reference to heat killing

Question 27

thermal death time (TDT)

Answer 27

**time required to kill all the bacteria in a culture at a specified temperature** - in reference to heat killing

Question 28

decimal reduction time (D value)

Answer 28

**length of time required to kill _90% of the organisms_ in a population at a specific temperature** - in reference to heat killing

Question 29

moist heat diagram

Answer 29

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Question 30

pasteurization

Answer 30

**goal is not to sterilize, but to _kill pathogens_** - without affecting the texture, color, or taste of the product **different time and temperature combinations can be used:** **1.** low temperature, long time (LTLT) **2.** high temperature, short time (HTST) **3.** ultra high temperature (UHT)

Question 31

cold methods to control microbial growth

Answer 31

- refrigeration, freezing - freeze-drying

Question 32

refrigeration, freezing

Answer 32

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

Question 33

freeze-drying

Answer 33

**freeze drying is used for _storing_ many microorganisms** - many microorganisms are sensitive to drying - but many are not

Question 34

physical control measures: filtration

Answer 34

**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 0.2μm can remove microbial cells, but not viruses from solutions** - to remove viruses, pore sizes of 20nm are necessary (1nm = 0.001μm)

Question 35

filtration diagram

Answer 35

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Question 36

physical control measures: sonication

Answer 36

**high frequency *ultrasound waves* to _disrupt cell structures_** - the disruption is achieved due to the _rapid changes in pressure within the intracellular liquid_

Question 37

physical control measures: irradiation

Answer 37

**method in which objects are bombarded with _high-energy electromagnetic radiation_** - e.g. ultraviolet (UV) light - e.g. gamma rays, electron beams, X-rays **foods do not become radioactive when irradiated** - any _reactive molecules_ produced when high-energy particles are _absorbed by food dissipate almost immediately_

Question 38

examples of foods & purpose approved for irradiation in the US

Answer 38

1963: wheat flower - control mold 1964: white potatoes - inhibit sprouting 1986: pork - kill trichina (Trichinella) parasites 1986: fruit and vegetables - control insects; increase shelf life 1986: herbs and spices - sterilize 1992: poultry - reduce numbers of bacterial pathogens 1997: meat - reduce numbers of bacterial pathogens 2006: shellfish - reduce numbers of Vibrio species and other pathogens 2010: lettuce and spinach - reduce numbers of bacterial pathogens

Question 39

efficacy of a given chemical agent depends on...

Answer 39

1. the presence of organic matter 2. the kinds of organisms present 3. corrosiveness 4. stability, odor, and surface tension

Question 40

efficacy of a given chemical agent: the presence of organic matter

Answer 40

**chemicals will bind to inert organic material** - lowering its effectiveness against microbes

Question 41

efficacy of a given chemical agent: the kinds of organisms present

Answer 41

ideally should be effective against a *broad range of pathogens*

Question 42

efficacy of a given chemical agent: corrosiveness

Answer 42

**should not corrode the surface** - nonliving or living

Question 43

efficacy of a given chemical agent: stability, odor, and surface tension

Answer 43

**stability** - should be stable upon storage **odor** - neutral or pleasant odor **surface tension** - low surface tension

Question 44

commercial disinfectants + groups

Answer 44

**used to reduce or eliminate microbial content from commercial products** _six different groups:_ **1.** ethanol, iodine, chlorine **2.** surfactants (such as detergents) **3.** aldehydes **4.** phenolics **5.** heavy metals **6.** peroxygens

Question 45

commercial disinfectant: ethanol, iodine, chlorine

Answer 45

highly reactive compounds - damages proteins, lipids, and DNA

Question 46

commercial disinfectant: surfactants (such as detergents)

Answer 46

**help in the mechanical removal of microbes from surfaces** - meaning you need to put in effort to mechanically disinfect

Question 47

commercial disinfectant: aldehydes

Answer 47

combines with **proteins and nucleic acids** - _inactivates them_

Question 48

commercial disinfectant: phenolics

Answer 48

denature **proteins** & disrupt **membranes** **Joseph Lister:** - carbolic acid (i.e. phenol) used for treatment of surgical wounds

Question 49

commercial disinfectant: heavy metals

Answer 49

binds to proteins - inhibit enzymatic activity e.g. copper, silver

Question 50

commercial disinfectant: peroxygens

Answer 50

**strong oxidizers** - produce free radicals that _damage cellular macromolecules_ *cellular macromolecules:* - nucleic acids, lipids, proteins, carbohydrates

Question 51

what type of sterilization should be used for disposable plasticware?

Answer 51

**gas sterilization (antimicrobial gases) OR gamma irradiation** - disposable plasticware such as petri dishes, syringes, sutures, and catheters are _not amenable to heat sterilization or chemical disinfection_

Question 52

antimicrobial gases

Answer 52

**used for gas _sterilization_** (e.g. ethylene oxide [EtO]) - destroys proteins by alkylation - microbicidal/sporicidal - rapidly penetrates packing materials, including plastic wraps - highly explosive

Question 53

bacterial resistance to disinfectants

Answer 53

**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_** - e.g. iodine **disinfectants that have _multiple targets at high concentrations_ may only have a _single target at low concentrations_** - a situation that can **_foster resistance_** - e.g. triclosan

Question 54

triclosan in hand soap

Answer 54

triclosan can find its way into wastewater and sewage systems from the handwashing process - this can then make its way into the bodies of amphibians and fish