Chapter 12: Microbial Control

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Fomites

Inanimate items, such as doorknobs, toys, or towels, which may harbor microbes and aid in disease transmission

First factor that influences the level of cleanliness required

the application for which the item will be used

Second factor that influences the level of cleanliness required

the level of resistance to antimicrobial treatment by potential pathogens

Clostridium botulinum

bacterium that produces the neurotoxin that causes botulism

sterilization

the complete removal or killing of vegetative cells, endospores, and viruses from the targeted item or environment

Where are sterilization protocols generally reserved for?

laboratory, medical, manufacturing, and food industry settings, where it may be imperative for certain items to be completely free of potentially infectious agents

Sterilants

chemicals that can be used to achieve sterilization; can also kill endospores

sterility

asepsis

aseptic technique

involves a combination of protocols that collectively maintain sterility, thus preventing contamination of the patient with microbes and infectious agents

sepsis

a systemic inflammatory response to an infection that results in high fever increased heart and respiratory rates, shock, and possibly death

sterile field

a designated area that is kept free of all vegetative microbes, endospores, and viruses

commercial sterilization

food sterilization protocol; uses heat at a temp low enough to preserve food quality but high enough to destroy common pathogens responsible for food poisoning

disinfection

inactivates most microbes on the surface of a fomite by using antimicrobial chemicals or heat

disinfectants

should be fast acting, stable, easy to prepare, inexpensive, and easy to use

vinegar

a natural disinfectant

chlorine bleach

used to clean nonliving surfaces

antiseptic

antimicrobial chemicals safe for use on living skin or tissues; examples: hydrogen peroxide and isopropyl alcohol; must also be selectively effective against microorganisms and able to penetrate tissue deeply w/o causing tissue damage

antisepsis

the process of applying an antiseptic

critical items

must be sterile because they are going to be used in the body and penetrate sterile tissues or the the bloodstream; catheters

semicritical

may contact mucous membranes or nonintact skin but do not penetrate tissues; GI endoscopes

noncritical

may contact but do not penetrate skin; bed linens, furniture, crutches

handwashing

an example of degerming

degerming

when microbial numbers are significantly reduced by gently scrubbing living tissue with a mild chemical to avoid the transmission of pathogenic microbes; removes most, but not all, microbes

sanitization

refers to the cleansing of fomites to remove enough microbes to achieve safe levels

-cide or -cidal

physical and chemical methods of microbial control that kill the targeted microorganism

bactericides

kills bacteria

viricides

kill or inactivate viruses

-stat or -static

do not kill organisms but stop their growth; make the population static

bacteriostatic

inhibits the growth of bacteria

fungistatic

inhibits the growth of fungi

what are -static treatments for?

they may not kill the infectious agent, but they are less toxic to humans, and therefore allow them to keep the microbial population of an item in check, while also not harming the individual using it as much as something stronger

microbial death curve

a curve used to evaluate the degree of microbial control and describe the progress and effectiveness of a particular protocol

decimal reduction time or D-Value

the amount of time it takes for a specific protocol to produce a one order-of-magnitude decrease in the number of organisms, or the death of 90% of the population

factors that can contribute to the effectiveness of a disinfecting agent or microbial control protocol

• length of time

• susceptibility of the agent to that disinfecting agent or protocol

• conditions that limit the contact between the agent and the targeted cell’s cells (bodily fluids, tissue, biofilms, mud

What type of medical item requires sterilization?

needles

What is suitable for use on tissues for microbial control to prevent infection?

antiseptic

What is the best microbial control protocol that inhibits the growth of molds and yeast?

fungistatic

The decimal reduction time refers to the amount of time it takes to what?

reduce a microbial population by 90%

Sanitization leaves an object free of microbes.

False

thermal death point (TDP)

the lowest temp at which all microbes are killed in a 10-minute exposure

thermal death time (TDT)

the length of time needed to kill all microorganisms in a sample at a given temperature

boiling

• one of the oldest methods of moist-heat control of microbes

• typically quite effective at killing vegetative cells and some viruses

• less effective at killing endospores

• may be less effective at higher altitudes

• no longer considered a useful sterilization technique in the lab or clinical setting

dry-heat sterilization

• typically involved in aseptic technique by using direct application of high heat

• can be applied for relatively high long periods of time

moist-heat sterilization

typically the more effective protocol because it penetrates cells better than dry heat does

autoclave

• rely on moist-heat sterilization

• used to raise items above the boiling point of water to sterilize items such as surgical equipment from vegetative cells, viruses, and endospores without damaging the items

• considered the most effective method of sterilization

• the air in the chamber is removed and replaced with increasing amounts of steam trapped in the enclosed chamber, resulting in inc. interior pressure and temps above the boiling point

Charles Chamberland (1851-1908)

designed the modern autoclave while working in the lab of Louis Pasteur

retorts

large industrial autoclaves that allow for moist-heat sterilization on a large scale

gravity displacement autoclaves

steam is introduced into the chamber from the top or sides and air is forced downwards into a vent

prevacuum sterilizers

air is removed completely using a vacuum before introducing steam into the chamber; steam can more easily penetrate wrapped items

pasteurization

kills pathogens and reduces the number of spoilage-causing microbes while maintaining food quality; most commonly used today to kill heat-sensitive pathogens in milk and other food products; not sterile, food will eventually spoil

high-temp short-time (HTST) pasteurization

exposes milk to a temp of 72 degC for 15 sec, which lowers bacterial numbers while preserving the quality of the milk

ultra-high-temperature

milk is exposed to a temp of 138 degC for 2+ sec; can be stored for along time in sealed containers without being refrigerated, but the proteins are altered, and the taste and smell alter slightly

psychrophiles

prefer cold temps

refrigeration

keeps temps between 0 and 7 degC which inhibits microbial metabolism, slowing the growth of microorganisms significantly and helping preserve refrigerated products

freezing below -2 degC

can stop microbial growth and even kill susceptible organisms

dry ice, ultra-low freezer, or liquid nitrogen

keeps things frozen at ultra-low temps of -70 degC

desiccation

drying or dehydration; removing water from microorganism so that it cannot metabolize

lyophilization

• freeze-drying; a method of desiccation in which an item is rapidly frozen and placed under a vacuum so that water is lost by sublimation

• combines both exposure to cold temperatures and desiccation

• better preserves the item’s original qualities

• can be stored at room temp if packaged appropriately

water activity

• the water content of foods and materials

• can be lowered w/o physical drying by the addition of solutes such as salts or sugars

high amounts of salts or sugars

create conditions of high osmotic pressure

radiation

can be used to kill microbes or inhibit their growth

ionizing radiation

• includes x-rays, gamma rays, and high-energy electron beams

• strong enough to pass into the cell where it alters molecular structures and damages cell components

• induces double-strand breaks in DNA molecules

x-rays and gamma rays

• easily penetrates paper and plastic so it can sterilize packaged materials

• used to sterilize materials that cannot be autoclaved

• also used for the sterilization of other types of delicate, heat-sensitive materials used clinically

gamma irradiation

used for food preservation in europe

nonionizing radiation

commonly used for sterilization and uses less energy than ionizing radiation; does not penetrate cells or packaging

thymine dimer

formed by UV light; can kill microorganisms through mutation formation

UV light

• commonly incorporated into water purification systems for use in homes

• germicidal lamps are used in surgical suites, biological safety cabinets, and transfer hoods

  • must be exposed directly to the cells

filtration

a method of physically separating microbes from samples

high-efficiency particulate air (HEPA) filters

have effective pore sizes of 0.3 µm small enough to capture bacterial cells, endospores, and many viruses as air goes through, nearly sterilizing the air on the other side; common in ventilation systems of buildings or rooms in hospitals

membrane filtration

can be used to remove microbes from liquid; to remove bacteria, it typically has a pore size of 0.2 µm; useful for heat-sensitive solutions

What term is used to describe the time required to kill all of the microbes within a sample at a given temperature?

thermal death time

What does not actually kill microbes or inhibit their growth but instead removes them physically from samples?

filtration

Ionizing radiation can penetrate surfaces, but nonionizing radiation cannot.

true

Moist-heat sterilization protocols require the use of higher temperatures for longer periods of time than do dry-heat sterilization protocols do.

false

phenol

• carbolic acid

• used by Joseph Lister as a disinfectant for the treatment of surgical wounds

Joseph Lawrence

was inspired by Lister’s work to develop Listerine, an alcohol-based mixture of several related compounds that is still used today as an oral antiseptic

phenolics/phenolic compounds

• chemical compounds found in antiseptic mouthwashes and throat lozenges

• tend to be stable, persistent on surfaces, and less toxic than phenol

• inhibits microbial growth by denaturing proteins and disrupting membranes

chemical composition of phenolic

consists of a benzene ring with a -OH group

thymol and eucalyptol

phenolics that occur naturally in plants

a

chemical structure of a phenol (carbolic acid)

b

o-Phenylphenol; a type of phenolic; has been used as a disinfectant as well as to control bacterial and fungal growth on harvested citrus fruits

c

hexachlorophene; a phenol; known as a bisphenol (two rings); is the active ingredient in pHisoHex

cresols

methylated phenols; active ingredient in various formulations of Lysol

o-phenylphenol

• active ingredient in various formulations of Lysol

• commonly used in agriculture to control bacterial and fungal growth on harvested crops, especially citrus fruits

hexachlorophene

• bisphenol

• a disinfectant

• active ingredient in pHisoHex, a topical cleansing detergent widely used for handwashing in clinical settings

• expose can lead to neurological problems

pHisoHex

• active ingredient is hexachlorophene

• particularly effective against gram-positive bacteria, including those causing staphylococcal and streptococcal skin infections

• was formerly used for bathing infants

triclosan

bisphenol compound which has been widespread in antibacterial products over the last decades; initially used in toothpaste; commonly used in soaps and impregnated into common items like cutting boards, knives particularly effective against gram-positive bacteria on the skin as well as certain gram-negative bacteria and yeasts

halogens commonly used for disinfection

iodine, chlorine, and fluorine

iodine

works by oxidizing cellular components including sulfur-containing amino acids, nucleotides, and fatty acids, and destabilizing macromolecules that contain these molecules; often used as a topical tincture, but may cause staining or skin irritation

iodophor

a compound of iodine complexed with an organic molecule, thereby increasing iodine’s stability and its efficacy

povidone-iodine

• a common iodophor

• includes a wetting agent that releases iodine relatively slowly

• betadine is a brand of this commonly used as a hand scrub by medical personnel before surgery and for topical antisepsis of a patient’s skin before incision

a

betadine

chlorine

a halogen commonly used for disinfection

chlorine gas

• mixed with water, it produces a strong oxidant called hypochlorous acid, which is uncharged and enters cells easily

• commonly used in municipal drinking water and wastewater treatment plants, with the resulting hypochlorous acid producing the antimicrobial effect

sodium hypochlorite

the chemical component of common household bleach

hypochlorite salts (including sodium and calcium hypochlorites)

commonly used to disinfect swimming pools

chlorine gas, sodium hypochlorite, and calcium hypochlorite

commonly used disinfectants in the food processing and restaurant industries to reduce the spread of foodborne diseases

chloramines

a class of chlorinated compounds widely used as disinfectants; relatively stable, releasing chlorine over long periods of time; derivatives of ammonia by substitution of one, two, or all three hydrogen atoms with chlorine atoms; may be used for disinfection of drinking water

sodium dichloroisocyanurate (NaDCC)

• can be used for drinking water disinfection

• are available for general use

chlorine dioxide

a gaseous agent used for fumigation and sterilization of enclosed areas; commonly used for the disinfection of water