Chapter 9: Physical and Chemical Control of Microbes (Microbial Control methods down to…)

What are the three types of microbial control methods? Which one of the three Is put into a separate category?

1. Physical agent

2. Chemical agent

3. Mechanical removal methods

• Mechanical removal methods is put into physical agents

Do a fill in the blank of the microbial control methods diagram

Of the microbial control methods what are the two pathways of physical agents? What is the further break down?

Physical agents ~> Heat and Radiation

1. Heat ~> Dry or Moist

• Dry heat ~> Incineration (Sterilization) or Dry Oven (Sterilization)

• Moist heat ~> Steam under pressure (Sterilization) or Boiling water/hot water/pasteurization (Disinfection)

2. Radiation ~> Ionizing or nonionizing

• Ionizing ~> X-ray/cathode/gamma (Sterilization)

• Nonionizing ~> UV (Disinfection)

Of the microbial control methods what are the two pathways of chemical agents? What is the further break down?

Chemical agents ~> Gases or Liquids

1. Gases ~> Sterilization (ex: ethylene oxide) or Disinfection (ex: CL2)

2. Liquids ~> Animate objects or inanimate objects

• Animate objects ~> Antisepsis

• Inanimate objects ~> disinfection or sterilization

Of the microbial control methods what are the two pathways of mechanical removal methods/agents? What is the further break down?

Filtration ~> air or liquids

• Air or liquids ~> Sterilization

For filtration can air or liquid always achieve sterilization? Provide an example of sterilization.

Yes air and liquid can always achieve sterilization when filtrated

• Ex: immuno. Compromised patients need sterile air

Are high or low temperatures microbicidal or microbistatic? What are the two methods of physical control when it comes to heat?

High temperatures are microbicidal, Lower temperatures are microbistatic

• There is moist heat or dry heat

What is moist heat and what is its effect? Also what are examples? What is dry heat and what is its effect? Also what are examples?

1. Moist heat:

• Penetrates the microbial cell better: lower temperatures and shorter exposure times to achieve the same effectiveness as dry heat

• Microbicidal effect is the coagulation and denaturation of proteins

• Examples: hot water, boiling water, or steam between 60°C and 135°C

2. Dry heat:

• Dehydrates the cell, removing water necessary for metabolic reactions

• Denatures proteins

• At very high temperatures, oxidizes cells, burning them to ashes

• Examples: hot air or an open flame (Bunsen burner), which ranges from 160°C to several

thousand degrees

What are the relative times between moist and dry heat? Which is not always convenient in a clinical setting? Do dry and moist heat always achieve sterilization?

• Dry heat is not always convenient in a clinical setting

• Moist heat has times like 3-15 mins depending on heat and dry heat is 1-10 hours

• Dry heat always achieves sterilization whereas moist heat doesn’t always achieve sterilization

Describe the resistance/sensitivity to heat between vegetative cells vs bacterial Endospores. Does heat apply uniformly across all bacteria types? Are pathogens more/less likely or neither susceptible than non pathogens?

• Bacterial endospores: Exhibit greatest resistance; Destruction of spores requires temperatures above boiling

• Vegetative cells: Vary in sensitivity to heat

• Pathogens are neither more nor less susceptible than nonpathogens

How do vegetative cells of endospore formers compare to non endospore forming cells when it come to heat? What is thermal death time and thermal death point?

• Vegetative cells of endospore formers are just as susceptible to heat as vegetative cells of non-endospore-formers

• Thermal death time (TDT): shortest length of time required to kill all test microbes at a specified temperature

• Thermal death point (TDP): the lowest temperature required to kill all microbes in a sample in 10 minutes

Describe boiling water of moist heat application and the effect it has on microbes. How long does it take to kill non-endospore-forming pathogens and what types does that include? Does it kill Endospores?

1. Boiling Water: Disinfection

• Exposing materials to boiling water for 30 minutes will kill most non-endospore-forming pathogens, including resistant species such as the tubercle bacillus (acid fast bacteria) and staphylococci.

• This method can be relied on only for disinfection and not for sterilization. (Does not kill Endospores)

Describe pasteurization of moist heat application and the effect it has on microbes. Does it sterilize, If not what does it achieve? It kills potential agents of what while retaining what? Is it safe for consumption and why don’t we sterilize food/liquids?

2. Pasteurization: Disinfection of Beverage

• For beverages such as milk, fruit juices, beer, and wine: heat is frequently used to reduce the microbial load and destroy pathogens.

• Pasteurization is a technique in which heat is applied to liquids to kill potential agents of infection and spoilage, while at the same time retaining the liquid’s flavor and nutritional value.

• Everything is safe for consumption and we don’t sterilize b/c it would change the taste

Describe stream under pressure for uses of moist heat application. What does it achieve? Only what two things is it ineffective in sterilizing and what would we use instead?

• Used on Heat-resistant materials such as glassware, cloth (surgical dressings), metallic instruments, liquids, paper.

• Achieves sterilization (no exceptions)

• However, it is ineffective for sterilizing substances that repel moisture (oils, waxes), or for those that are harmed by it (powders).

What are the two examples of dry heat application? Describe them and the differences plus provide examples if possible.

Dry heat: incineration or dry hot air oven

1. Incineration: flame of Bunsen burner up to 1800 degrees clerics and furnaces/incinerators 800-6500 degrees Celsius (short time)

• Incinerators burn things to ashes and it’s important for biohazard waste

2. Dry Hot air oven

• Hot air oven provides dry-heat that sterilizes

• Has a longer exposure to reach sterilization at 150-180 degrees Celsius for 2-4 hrs

Are the effects of cold temperatures -cidal or -static? What are most microbes not adversely affected by? What temperatures can preserve cultures of microbes? Does low temperatures ever achieve sterilization?

• To slow the growth of microbes in food during processing and storage: static effect, not cidal

• Most microbes are not adversely affected by gradual cooling, long-term refrigeration, or deep-freezing

• Temperatures from −70°C to −135°C can preserve cultures of bacteria, viruses, and fungi for long periods

• Never achieves sterilization

What is desiccation? Is it bacteristatic or bactericidal? Are the microbes killed or preserved or what? Why is dehydration important to cells?

Desiccation:

• Microbial Vegetative cells become dehydrated

• Many microbes are not killed and some are even preserved (static effect, not cidal)

• Dehydration is importnat because water is important for all enzymes

What is lyophilization the combination of? Is it bacteristatic or bactericidal? What is it a method of? What happens to pure cultures that go through this process?

• Combination of freezing and drying

• Method of preserving microorganisms in a viable state for many years

• Pure cultures are frozen instantaneously and exposed to a vacuum that removes water, avoiding the formation of ice crystals

• It is bacteristatic

What are the two types of radiation? What type of rays do they consist of? What is their effect on microbes?

There is ionizing radiation or nonionizing radiation

• Ionizing: gamma rays and x rays; achieves sterilization on microbes

• Nonionizing: ultraviolet rays; disinfects microbes

What is ionizing radiation? What does it achieve and it’s important for what type of materials? Where are items placed when undergoing this?

Ionizing radiation: gamma and x-rays

• Effective alternative for sterilizing materials that are sensitive to heat or chemicals

• Items are placed in machines that emit these rays and irradiated for a short time with a carefully chosen dosage

What is nonionizing radiation? What does it achieve if what? what does it pass though? What is it not as good as compared to ionizing radiation?

Nonionizing radiation: ultraviolet rays

• UV radiation is not as penetrating as ionizing radiation

• UV radiation readily passes through air, slightly though liquids and poorly through solids

• Object is disinfected if directly exposed for the full effect

What is filtration an effective method for? Is it -cidal/-static/or neither? What does it do mechanically? Describe how fluid is strained. What controls the level of sterilization?

• Effective method to remove microbes from air and liquids

• Is neither -static or -cidal and mechanically separates microbes

• Fluid is strained through a filter with openings large enough for the fluid to pass, but too small for microbes: Pore sizes can be controlled to permit true sterilization by trapping viruses or large proteins

What is filtration used to prepare? What are examples of filtration by air?

• Used to prepare liquids that cannot withstand heat such as serum, blood products, vaccines, drugs, IV fluids, enzymes, and media

• High-efficiency particulate air (HEPA) filters are used in hospital rooms/ sterile rooms

What is osmotic pressure/What do we do to create osmotic pressure? What does it create and cause? What is is similar to and microbes can’t do what as a result?

• Its a difference in solute concentrations and is created by Adding large amounts of salt or sugar to foods

• Creates a hypertonic environment for bacteria, causing plasmolysis (loss of cytoplasmic water

• Similar to dehydration and results in microbes not being able to perform metabolic activities

What are examples of osmotic pressure being used in history? Can osmotic pressure ever achieve sterilization? Is it -static or -cidal?

• Pickling, smoking, and drying foods have been used for centuries to preserve foods

• Osmotic pressure is never a sterilizing technique (bacteriostatic)

Top Hat Question: What physical control methods would be used to sterilize the following items? 1. Inoculating loop 2. Glassware contaminated with bacteria 3. Vaccines 4. Powders and oils

1. Bunsen burner

2. Autoclave or steam under pressure

3. Filtration

4. Dry heat