Microbiology Chapter 11

Practical Concerns in Microbial Control questions to ask

Does the item in question 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 suitable for a given application? Will the agent penetrate to the necessary extent? Is the method cost- and labor-efficient, and is it safe?

Radiation:

Energy emitted from atomic activities and dispersed at high velocity through matter or space

Critical medical devices:

Expected to come into contact with sterile tissues

Fungistatic chemicals:

Inhibit fungal growth

Other effects on proteins:

Metallic ions bind to the active site, preventing it from interacting with its substrate

Bacteristatic agents:

Prevent the growth of bacteria on tissues or objects in the environment

Heat is the most widely used method of microbial control. Other methods:

Radiation Filtration Ultrasonic waves Cold

Sanitization:

Sanitization: -Any cleansing technique that mechanically removes microbes and debris -Reduces contamination to safe levels -Sanitizer: a soap or detergent used to sanitize

Aseptic techniques:

Sterile methods that exclude all microbes

Examples of Sterilized products are essential to human well-being.

Surgical instruments Syringes Commercially packaged foods

Thermal death point:

The lowest temperature required to kill all microbes in a sample in 10 minutes

Agents That Alter Protein Function Native state:

The normal three-dimensional configuration of a protein that allows proper function

Thermal death time:

The shortest length of time required to kill all test microbes at a specified temperature

Disinfection

The use of a physical process or a chemical agent (disinfectant) to destroy vegetative pathogens but not bacterial endospores. ---Disinfectants are normally only used on inanimate objects

Noncritical medical devices:

Those that do not touch the patient or are only expected to touch intact skin

________ is disinfection on a living surface.

antisepsis

Antisepsis Asepsis:

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

Aseptic techniques: Antisepsis:

application of chemical agents (antiseptics) to exposed body surfaces and surgical incisions to destroy or inhibit vegetative pathogens

Concept Check Describe the difference between a bactericidal agent and a bacteristatic agent.

bacteriostatic means limiting the growth of bacteria, while bactericidal means "killing" bacteria

Germicide and microbicide:

chemical agents that kill microorganisms

Concept Check List and describe four factors that affect microbial death rate.

cidal-kills bacteria static- stops the movement of bacteria -number of microbes -presence of organic matter in human wastes -temperature -fats and proteins -pH -time of exposure to agent -specific characteristics of the microorganism

Disinfection:

destroys most microbial life, reducing contamination on inanimate surfaces.

Virucide:

inactivates viruses, especially on living tissue

Fungicide:

kills fungal spores, hyphae, and yeasts

Put the following in order from most resistant to least resistant: Fungal spores Protozoan cysts Gram positive bacteria Prions

prions Protozoan cysts Fungal spores Gram positive bacteria

Sterilization:

the destruction of all microbial life.

Antisepsis Sepsis:

the growth of microorganisms in blood and other tissues.

Nonionizing Radiation: UV Rays Ultraviolet (UV) radiation:

--Ranges from 100 nm to 400 nm --Most lethal from 240 nm to 280 nm (peak at 260 nm) --Germicidal lamp: generates 254 nm --Not as penetrating as ionizing radiation

Lyophilization:

-A combination of freezing and drying -Common method of preserving microbes and other cells in a viable state -Pure cultures are frozen instantaneously and exposed to a vacuum that removes Chilling, freezing and desiccation are not methods of disaffection and sterilization of microbes

Dry heat:

-Air with a low moisture content that has been heated by a flame or electric heating coil -Temperature ranges from 160°C to several thousand degrees Celsius -Lack of water increases stability of some protein configurations, necessitating higher temperatures -At high temperatures, dry heat oxidizes cells, burning them to ashes

Antisepsis:

-Also called degermation -The same as disinfection, but on a living surface

Heat Resistance and Thermal Death

-Bacterial endospores exhibit the greatest resistance to disinfection methods. ---Destruction of spores usually requires temperatures above boiling ---Resistance varies -Vegetative cells vary in their sensitivity to heat.

Susceptibility of Microbes to Heat Tempature and length

-Both temperature and length of exposure should be considered for adequate sterilization. ---Higher temperatures allow shorter exposure times ---Lower temperatures require longer exposure times

The Effects of Cold and Desiccation

-Cold treatment merely retards the activities of most microbes. ---Some microbes are killed by cold temperatures ---Most are not adversely affected by gradual cooling, long-term refrigeration, or deep freezing

Relative Resistance of Microbial Forms: Bacterial endospores:

-Considered the most resistant microbial entities -Destruction of endospores is the goal of sterilization -Any process that will kill endospores will invariably kill less resistant microbial forms -Other methods of control (disinfection, antisepsis) act on microbes that are less hardy than endospores

Damage to the cell wall:

-Damage to the cell wall: -Blocking cell wall synthesis -Digesting the cell wall -Breaking down the surface of the cell wall -A cell with a damaged cell wall is fragile and becomes lysed easily. -Detergents and alcohols disrupt the cell wall

Desiccation

-Dehydration of vegetative cells directly exposed to normal room air -Some delicate pathogens can be killed by desiccation. -Some pathogens can be preserved upon desiccation. -Desiccation can preserve foods.

Nonionizing radiation:

-Excites atoms, raising them to a higher energy state -Leads to the formation of abnormal bonds within molecules such as DNA

Radiation suitable for microbial control:

-Gamma rays -X rays -Ultraviolet radiation

Death of microscopic organisms: Factors

-Harder to detect -No conspicuous vital signs -Lethal agents do not alter the overt appearance of microbial cells -Loss of movement cannot be used to indicate death -Special qualifications are needed to define and delineate microbial death

Moist heat:

-Hot water, boiling water, steam -Temperature ranges from 60°C to 135°C -Operates at lower temperatures and shorter exposure times than dry heat -Most microbicidal effect is coagulation and denaturation of proteins to permanently halt microbial metabolism

Cold sterilization:

-Ionizing radiation used as an effective alternative for sterilizing materials -Used for materials sensitive to heat or chemicals

Agents that Affect Protein and Nucleic Acid Synthesis

-Microbial cells depend on an orderly and continuous supply of proteins. ---Substances that inhibit ribosomes will also inhibit protein synthesis -Nucleic acids are necessary for the continued functioning of microbes ---Agent that impedes the transcription of DNA replication or DNA transcription or changes the genetic code is antimicrobial

Relative Resistance of Microbial Forms Primary targets of microbial control:

-Microorganisms capable of causing infection or spoilage -Constantly present in the external environment and on the human body -Often contains mixtures of microbes

Denaturation of proteins: Moist heat:

-Moist heat: irreversible solidification of an egg white when boiled -Strong organic acids and phenolics

Factors That Affect Death Rate

-Number of microorganisms -Nature of the microbes in the population -Type of microbial growth -Temperature and pH of the environment -Concentration of the agent -Mode of action of the agent -Presence of solvents, interfering organic matter, and inhibitors

Cell Membrane Surfactants:

-Polar molecules with hydrophilic and hydrophobic regions -Physically bind to the lipid layer and penetrate the internal hydrophobic region of membranes -This opens up leaky spots that allow injurious chemicals to seep into the cell and important ions to leak out

Ionizing radiation:

-Radiation ejects orbital electrons from an atom, causing ions to form -Causes the most damage to proteins

Antisepsis/degermation:

-Reduction of the number of microbes on the skin -Involves scrubbing the skin or immersing it in chemicals, or both -Emulsifies oils on the outer cutaneous layer -Mechanically removes potential pathogens on the outer layers of the skin

How Agents Affect the Cell Membrane

-The cell membrane and viral envelope are composed of lipids and proteins. -Disruption of the cell membrane causes: ---Loss of selective permeability ---Loss of vital molecules ---Allows the entry of damaging chemicals

How Antimicrobial Agents Work Cellular targets of physical and chemical agents:

-The cell wall -The cell membrane -Cellular synthetic processes (DNA, RNA) -Proteins

Agents That Alter Protein Function Denature:

: Disruption of proteins, rendering them nonfunctional Breaking of the bonds that maintain the secondary and tertiary structure

Bactericide:

A chemical that destroys bacteria except for those in the endospore stage

Sterilization

A process that destroys or removes all viable microorganisms, including viruses. ---Any material that has been subjected to this process is said to be sterile

Decontamination:

Also called sanitization The mechanical removal of most microbes from an animate or inanimate surface

Sporicide:

Bactericide: A chemical that destroys capable of killing endospores

Irradiation:

Bombardment of microbes with radiation

Concept Check What are the four cellular targets of physical and chemical agents?

Cell wall, cell membrane, cellular synthetic processes (DNA, RNA), protein

Microbistatic agents:

Chemicals used to control microorganisms in the body (antiseptics and drugs)

Semicritical medical devices:

Come into contact with mucosal membranes