Ch.9 Physical & Chemical control of Microbes

The methods of microbial control used outside the body are designed to result in four possible outcomes.

1. sterilization

2. Disinfection

3. Decontamination/Sterilization

4. Antisepsis/Degemination

The primary targets of microbial control are

microorganisms capable of causing infection or spoilage in the environment or human body.

traditionally considered the most resistant microbial entities

bacterial endospores

the goal of any sterilization process is

destruction of bacterial endospores

any process that kills endospores will invariably kill

all less resistant microbial forms.

Sterilization and disinfection are

processes

Agents used in processes

Bactericide, fungicide, virucide, sporicide, germicide/microbicide, Sepsis, and Asepsis

Bactericide

a chemical that destroys bacteria except for those is the endospore stage.

Fungicide

A chemical that can kill fungal spores, hyphae, yeasts

Virucide

A chemical known to inactivate viruses, especially on living tissues.

Sporicide

An agent capable of destroying bacterial endospores

Germicide/Microbicide

Chemical agents that kill microorganisms

Sepsis

The growth of microorganisms in the blood & other tissues

Asepsis

Any practice that prevents the entry of infectious agents into sterile tissues & thus prevents infection

Aseptic technique

practiced in health care; range from sterile methods to antisepsis

Antiseptics

Chemical agents applied directly to exposed body surfaces (skin & mucous membranes), wounds, & surgical incisions to prevent vegetative pathogens

Stasis and Static mean

to stand still

Bacteristatic

Chemical agents that prevent the growth of bacteria on tissues or on objects in the environment

Fungistatic

Chemicals that inhibit fungal growth

What has microbistatic effects because microbicidal compounds can be toxic to human cells.

Antiseptic and Drugs

Note

a -cidal agent does not necessarily result in sterilization, depending on how it is used.

Expected to come into contact with sterile tissues; must be sterilized before use

Critical medical devices

come into contact with mucosal membranes; must receive heigh-level disinfection, preferably sterilized

Semi critical devices

Do not touch the patients or only touch intact skin; require only low-level disinfection unless they become contaminated with blood or bodily fluids.

Noncritical devices

Death

permanent terminations of an organism’s vital process

Death is difficult to determine because

microbes have no conspicuous vital process

Microbiology definition of Death

permanent loss of reproductive capability even under optimum growth conditions

Least selective agents

tend to be effective against the widest range of microbes (heat & radiation)

Selective agents

targets only a single cellular component (drug)

Cellular targets of of physical & chemical agents

Cell wall, cytoplasmic membrane, cellular synthetic process (DNA, RNA), and proteins

Elevated temperatures are

microbicidal

lower temperatures are

microbistatic

Moist heat

Operates at lower temp. & shorter exposure times to achieve the same effectiveness as dry heat. Hot water, boiling water, and steam between 60 C & 135 C

Dry heat

Dehydrates the cell, removing water necessary for metabolic reactions; denatures proteins; increases the stability of some protein conformations, requiring higher temperatures. Hot air or an open flame, which ranges from 160 C to several thousand C

Bacterial endospores

exhibit greatest resistance; destructions of spores require temp. above boiling

Vegetative cells

vary in sensitivity to heat; death times vary

Thermal Death Time (TDT)

shortest length of time required to kill all test microbes at specified temperatures

Thermal Death Point (TDP)

the lowest temperature required to kill all microbes in a sample in 10 min.

Principle benefit of cold treatment

to slow growth of cultures & microbes in food during processing and storage.

Desiccation

vegetative cells directly exposed to normal room temp. gradually become dehydrated. Some are killed by this and many others are not and can even be preserved.

Lyophilization

combination of freezing and drying; method of preserving microorganisms in a viable state for many years.

Something worth noting

things that can form endospores can exist in the vegetative state.

Ionizing radiation

a highly effective alternative for sterilizing materials that are sensitive to heat or chemicals

Filtration

effective method to remove microbes from air and liquids

Uses for filtration

To prepare for liquids that cannot withstand heat such as serum, blood products, vaccines, drugs, IV fluids, enzymes, and media.

Aqeuous

chemicals dissolved in pure water as the solvent

Tinctures

chemicals dissolved in pure alcohol or alcohol-water mixture

High-level

germicides kill endospore and can be used as sterilant

Intermediate level

germicides kill fungal, but not bacterial spores, resistant pathogens, and viruses

Low-level

germicides eliminate only vegetative bacteria, vegetative fungal cells, and some viruses.

Dilutions

a small volume of the liquid chemical is diluted in a larger volume of solvent to achieve a certain radio.

parts per million

used for solutions such as chlorine that are effective in very diluted concentrations

percentage solutions

solute is added to water by weight of volume

sterilization

A process that completely destroys or removes all viable microorganisms, including viruses and bacterial endospores. It is reserved for inanimate objects

Disinfection

A physical process or chemical agent that destroys vegetative pathogens, but not bacterial endospores. Used primarily on inanimate objects

Decontamination/sanization

A cleansing technique that mechanically removes microbes and debris to reduce contamination to safe public health levels

Antisepsis/degermination

A form of decontamination practiced on living tissues (such as human skin) to reduce microbial numbers