Micro Ch. 9 (Physical and Chemical Control of Microbes)

Disinfection

Physical process to destroy vegetative pathogens but not bacterial endospores. Removes harmful products of microorganisms (toxins) from material. Normally used on inanimate objects because the concentration required to be effective is harmful to human tissue. Common uses: boiling food utensils, applying 5% bleach solution to an examining table, immersing thermometers in an iodine solution between uses. [Bleach, Iodine, Heat (boiling)]

surfactants/detergents

Positively charged end of the molecule binds well with the predominantly negatively charged bacterial surface proteins. Long, unchained hydrocarbon chain allows the chemical to disrupt the cytoplasmic membrane. Cytoplasmic membrane loses selective permeability, causing cell death.

Sterilization

Process that destroys or removes all viable microorganisms (including viruses). The term should be used only in the strictest sense. Generally reserved for inanimate objects as it would be impractical or dangerous to use this process parts of the human body. Common uses: surgical instruments, syringes, commercially packaged food. [Heat (autoclave), Sterilants (chemical agents capable of destroying spores)]

Choice of a chemical compound (name 2)

Rapid action in low concentrations, solubility and long-term stability, broad-spectrum microbicidal action with selective toxicity, penetration, resistance to inactivation, noncorrosive and nonstaining, sanitizing and deodorizing properties, affordability and accessibility. Two compounds: Hydrogen peroxide and Glutaraldehyde

Degermation/Antisepsis

Reduces the number of microbes on the human skin. A form of decontamination but on living tissues. Involves scrubbing the skin (mechanical friction) or immersing it in chemicals (or both). [Alcohol, Surgical hand scrubs]

Be able to differentiate the effects of a static vs. cidal compound

Static = "to stand still", cidal = "to kill"

End goal of sterilization

The destruction of bacterial endospores.

Sepsis

The growth of microorganisms in the blood and other tissues.

Factors affecting microbial death rate

The number of microbes (Higher load of contaminants takes longer to destroy). The nature of the microorganisms in the population. Temperature and pH of the environment. The concentration (dose, intensity) of the agent. The mode of action of the agent: How does it kill or inhibit the microorganism? The presence of solvents, interfering organic matter, and inhibitors (Saliva, blood, and feces can inhibit the action of disinfectants).

Effects of desiccation

Vegetative cells directly exposed to normal room temperature gradually become dehydrated. Some microbes are killed, on others it has no effect.

4 targets of physical and chemical agents

cell wall cell membrane cellular synthetic processes proteins

Germicide/microbicide

chemical agents that kill microorganisms

Dry heat

hot air or an open flame, ranges from 160°C to thousands of degrees Celsius. Dehydrates the cell, removing water necessary for metabolic reactions. Denatures proteins. At very high temperatures, oxidizes cells, burning them to ashes. Less effective than moist heat.

Moist heat

hot water, boiling water, or steam-between 60°C and 135°C. Operates at lower temperatures and shorter exposure times to achieve the same effectiveness as dry heat. Microbicidal effect is the coagulation and denaturation of proteins.

aqueous solution vs tincture

pure water as the solvent vs alcohol or water-alcohol mixtures as the solvent.

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

Microbes most resistant to destruction (Slide 7)

(most resistant) Prions Bacterial endospores Mycobacterium Staphylococcus and Pseudomonas Protozoan cysts Protozoan trophozoites Most gram-negative bacteria Fungi and fungal spores Nonenveloped viruses Most gram-positive bacteriaLess resistant (least resistant) Enveloped viruses

Agents of microbial control

*Physical:* Heat (dry, moist), Radiation, (ionizing, nonionizing) *Chemical:* Gaseous & liquid agents *Mechanical:* Filtration

Disinfectant

A chemical agent intended for the removal of vegetative pathogens but not bacterial endospores. Usually used only on inanimate objects.

Osmotic Preservation

Adding large amounts of salt or sugar to foods creates a hypertonic environment for bacteria, causing plasmolysis. Pickling, smoking, and drying foods have been used for centuries to preserve foods. Osmotic pressure is never a sterilizing technique.

Sporicide

An agent capable of destroying bacterial endospores.

Antisepsis

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

Antiseptic

Chemical agent applied directly to exposed body surfaces (skin and mucous membranes), wounds, and surgical incisions to prevent vegetative pathogens. Preparing the skin before surgical incisions with iodine compounds, swabbing an open root canal with hydrogen peroxide, ordinary hand washing with a germicidal soap.

Virucide

Chemical known to inactivate viruses, especially on living tissue.

Fungicide

Chemical that can kill fungal spores.

Bactericide

Chemical that destroys bacteria except for those at the endospore stage

Decontamination/Sanitization

Cleansing technique that mechanically removes microorganisms as well as other debris to reduce contamination to safe levels. Important to restaurants, dairies, breweries, and other commercial entities that handle large numbers of soiled utensils/containers. Common uses: cooking utensils, dishes, bottles, and cans must be sanitized for reuse. [Soaps, Detergents, Commercial dish washers]

Lyophilization

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.

disinfectant vs. antiseptic

Disinfectant kills up to and including vegetative pathogens, but not bacterial endospores. Antiseptics reduce bacteria to safe concentrations.

Pasteurization

Disinfection of beverages through moist heat.

Factors considered for proper microbial treatment

Does the application require sterilization, or is disinfection adequate? Is the item to be reused or permanently discarded? If it will be reused, can the item withstand heat, pressure, radiation, or chemicals? Is the control method appropriate for a given application? In the case of a chemical, will it leave an undesirable residue? Will the agent penetrate to the necessary extent? Is the method cost- and labor-efficient and is it safe?

Filtration

Effective method to remove microbes from air and liquids. Fluid is strained with openings large enough for the fluid to pass, too small for microbes. Thin membranes of cellulose acetate, polycarbonate, and plastics whose pore size is carefully controlled, charcoal, diatomaceous earth, or unglazed porcelain are also used. Pore sizes can be controlled to permit true sterilization by trapping viruses or large proteins. Used to prepare liquids that cannot withstand heat (serum, blood products, vaccines, drugs, IV fluids, enzymes, and media). Alternative method for decontaminating milk and beer without altering its flavor. Important step in water purification. Unable to remove soluble molecules (toxins) that can cause disease. High efficiency particulate air (HEPA) filters are used in hospital rooms and sterile rooms.

Radiation (ionizing and non-ionizing)

Energy emitted from atomic activities and dispersed at high velocity through matter or space. Nonionizing: ultraviolet, leads to disinfection. Ionizing: X-ray, gamma, cathode, leads to sterilization.

low level, intermediate and high level germicide

High-level germicides kill endospores and are sterilizing. Intermediate-level germicides kill fungal spores and some resistant pathogens and viruses. Low-level germicides eliminate only vegetative cells and some viruses.

selectivity as it applies to treatments

Least selective agents tend to be effective against the widest range of microbes (heat and radiation). Selective agents target only a single cellular component (drugs).

Cellular effects of cold temperatures

Microbistatic. Principal benefit is to slow growth of cultures and microbes in food during processing and storage. Merely retards the activities of most microbes, most 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.

Microbial "death"

Permanent termination of an organism's vital processes. *Permanent loss of reproductive capability*, even under optimum growth conditions has become the accepted microbiological definition.