Chapter 9: Controlling Microbial Growth in the Environment

Antisepsis

Reduction in the number of microorganisms and viruses, particularly potential pathogens, on living tissue

Example of antisepsis

Use of iodine or alcohol to prepare skin for an injection

T o F: Antiseptics are frequently sterilizers whose strength has been reduced to make them safe for living tissues

False; they are disinfectants

Aseptic

Refers to an environment or procedure free of pathogenic contaminants

Example of aseptic

Preparation of surgical field; hand washing; flame sterilization of laboratory equipment

-cide, -cidal

Suffixes indicating destruction of a type of microbe

Examples of -cide, -cidal

Bactericide; fungicide; germicide; virucide

T o F: Germicides include ethylene oxide, propylene oxide, and aldehydes

True

Degerming

Removal of microbes by mechanical means

Examples of degerming

Hand washing; alcohol swabbing at site of injection

T o F: Chemicals play a primary role to the mechanical removal of microbes

False; they play a secondary role

Disinfection

Destruction of most microorganisms and viruses on nonliving tissue

Example of disinfection

Use of phenolics, alcohols, aldehydes, or soaps on equipment or surfaces

T o F: The term is used primarily in relation to eukaryotes

False; for prokaryotes

Pasteurization

Use of heat to destroy pathogens and reduce the number of spoilage microorganisms in foods and beverages

Examples of pasteurization

Pasteurized milk and fruit juices

T o F: Heat treatment is brief to minimize alteration of taste and nutrients; microbes remain and eventually cause spoilage

True

Sanitization

Removal of pathogens from objects to meet public health standards

Example of sanitization

Washing tableware in scalding water in restaurants

T o F: Standards of sanitization are the same among all governmental jurisdictions

False; they vary among different jurisdictions

-stasis, -static

Suffixes indicating inhibition but not complete destruction of a type of microbe

Examples of -stasis, -static

Bacteriostatic; fungistatic; virustatic

T o F: Germistatic agents include some chemicals, refrigeration, and freezing

True

Sterilization

Destruction of all microorganisms and viruses in or on an object

Sterilization example

Preparation of microbiological culture media and canned food

T o F: Sterilization is typically achieved by steam under pressure, by incineration, or by ethylene oxide gas

True

Microbial death

Permanent loss of reproductive ability under ideal environmental conditions

Microbial death rate

Often constant for a microorganism under particular set of conditions

Antimicrobial agents target

Cell wall, cell membrane, DNA/RNA, proteins

The cell wall maintains

Shape and integrity

T o F: Cell lysis occurs when the cell wall/membrane is damaged by antimicrobial agents

True

T o F: Viruses without an outer envelope (nonenveloped viruses) are tougher and can survive harsher environments better than those with envelopes

True

Protein function depends on ____ __________

3D shape

Denaturation

Loss of normal shape of a protein due to extreme heat or certain chemicals

Chemicals, radiation, and heat can alter or destroy nucleic acids, causing _____________ or ___________ of protein synthesis

Mutations; inhibition

Ideally, agents for the control of microbes should be (4)

- Inexpensive

- Fast-acting

- Stable during storage

- Capable of controlling microbial growth while being harmless to humans, animals, and objects

3 main actors affecting the efficacy of antimicrobial methods

1. Site to be treated

2. Relative susceptibility of microorganisms

3. Environmental conditions

How can the site to be treated affect the efficacy of antimicrobial methods?

Harsh chemicals and extreme heat cannot be used on humans, animals, and fragile objects

How can the relative susceptibility of microorganisms affect the efficacy of antimicrobial methods?

Some microbes are naturally more resistant than others

Low-level germicides kill

Vegetative bacteria, fungi, protozoa, and some viruses

Intermediate-level germicides kill

Kill fungal spores, protozoan cysts, viruses, and pathogenic bacteria

High-level germicides kill

All pathogens, including endospores

How can environmental conditions affect the efficacy of antimicrobial methods? (2)

- Temperature and pH

- Organic materials

How can temperature and pH affect the efficacy of antimicrobial methods?

Higher temperatures and optimal pH levels usually increase the effectiveness of antimicrobial methods by enhancing chemical reactions and damaging microbes faster

How can organic materials (blood, pus, feces) affect the efficacy of antimicrobial methods?

Can decrease the efficacy of antimicrobial methods because they protect microbes by forming a barrier and inactivate disinfectants by reacting with the chemicals

Biosafety level 1 (BSL-1)

Handling pathogens that do not cause disease in healthy humans

Biosafety Level 2 (BSL-2)

Handling moderately hazardous agents

Biosafety Level 3 (BSL-3)

Handling microbes in safety cabinets

Biosafety Level 4 (BSL-4)

Handling microbes that cause severe or fatal disease

6 physical methods of microbial control

1. Heat-related methods

2. Refrigeration and Freezing

3. Desiccation and Lyophilization

4. Filters

5. Osmotic pressure

6. Radiation

3 effects of high temperatures

1. Denature proteins

2. Interfere with integrity of cytoplasmic membrane and cell wall

3. Disrupt structure and function of nucleic acids

Thermal death point

Lowest temperature that kills all cells in broth in 10 minutes

Thermal death time

Time to sterilize volume of liquid at set temperature

2 heat-related methods for microbial control

1. Moist heat

2. Dry heat

4 uses for moist heat

1. Disinfect

2. Sanitize

3. Sterilize

4. Pasterize

Moist heat will

Denature proteins and disrupt cytoplasmic membranes

Moist heat is

More effective then dry

1 multiple choice option

4 methods of microbial control using moist heat

1. Boiling

2. Autoclaving

3. Pasteurization

4. Ultra-high-temperature sterilization

Boiling kills

Vegetative cells of bacteria and fungi, protozoan trophozoites, and most viruses

2 multiple choice options

T o F: Boiling time is critical; different elevations require different boiling times

True

Autoclaving

Method of sterilization using steam under pressure

Boiling temperature __________ as pressure ___________

Increases; increases

2 multiple choice options

Pasturization

Treating a substance with heat to kill or slow the growth of pathogens

T o F: Pasteurization is sterilization

False

Ultra-high-temperature sterilization

140C for 1-3 seconds, then rapid cooling

Dry heat is

Used for materials that cannot be sterilized with moist heat

Dry heat is different from moist heat in that (3)

- It kills microbes by oxidation

- Requires higher temperatures and longer exposure times

- Does not penetrate materials as effectively

_______________ is ultimate means of sterilization

Incineration

How does refrigeration control microbial growth?

It decreases microbial metabolism, growth, and reproduction

T o F: Refrigeration halts growth of most microbes

True

T o F: No microbes are capable of multiplying in refrigerated food

False

_______ freezing is more effective then ________ freezing

Slow; quick

Desiccation (drying)

Inhibits growth due to removal of water

Lyophilization (freeze-drying)

Used for long-term preservation of microbial cultures, prevents formation of damaging ice crystals

How do filters control microbial growth?

Through physically removing microbes from air or liquids, especially when heat can't be used

How does osmotic pressure affect microbial growth?

High salt or sugar creates a hypertonic environment that dehydrates cells (water follows solutes); fungi tolerate it better than bacteria

How does radiation affect microbial growth?

Damages DNA

How does ionizing radiation affect microbial growth?

Creates ions that break chemical bonds and denature DNA, killing microbes—gamma rays penetrate well but take longer

How does nonionizing radiation affect microbial growth?

Causes DNA damage (pyrimidine dimers) but has poor penetration, so it's mainly used to disinfect surfaces and air

11 chemical methods of microbial control

1. Phenol

2. Phenolics

3. Alcohols

4. Halogens

5. Oxidizing agents

6. Surfactants

7. Heavy metals

8. Aldehydes

9. Gaseous agents

10. Enzymes

11. Antimicrobials

Phenol (carbolic acid) use in microbial control

Original surgical antiseptic; now replaced by less odorous and injurious phenolics

Phenolics (chemically altered phenol) use in microbial control

Disinfectants and antiseptics

Alcohols use in microbial control

Disinfectants, antiseptics, and as asolvent in tinctures

Halogens use in microbial control

Disinfectants, antiseptics, and water purification

Oxidizing Agents use in microbial control

Disinfectants, antiseptics for deep wounds, water purification, and sterilization of food processing and medical equipment

Surfactants use in microbial control

Soaps: degerming; detergents:antiseptic

Quaternary Ammonium Compounds (Quats) are

Surfactants

Quaternary Ammonium Compounds (Quats) use in microbial control

Disrupt microbial cell membranes, causing leakage and cell death

Heavy Metals use in microbial control

Fungistats in paints; silver nitrate cream: surgical dressings, burn creams, and catheters; copper: algicide in water reservoirs, swimming pools, and aquariums

Aldehyde use in microbial control

Disinfectant and embalming fluid

Gaseous Agents use in microbial control

Sterilization of heat- and water-sensitive objects

Enzyme use in microbial control

Removal of prions on medical instruments

Antimicrobials

Disinfectants and treatment of infectious diseases

Method for Evaluating Disinfectants and Antiseptics

Phenol coefficient

Phenol coefficient

Compares disinfectant's effectiveness to phenol

Greater then _____ indicates agent is more effective then phenol

1.0