Microbiology Chapter 11

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

Bacteristatic agents:

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

Modes of action of germicides are to attack cellular targets:

Proteins Nucleic acids Cell wall Cell membrane

Ionizing radiation:

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

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

Desirable qualities of a germicide:

Rapid action in low concentrations Solubility in water or alcohol and long-term stability Broad-spectrum microbicidal action without toxicity to human and animal tissues Penetration of inanimate surfaces to sustain a cumulative or persistent action Resistance to becoming inactivated by organic matter Noncorrosive or nonstaining properties Sanitizing and deodorizing properties Affordability and ready availability

Aqueous solutions:

Solutions containing pure water as the solvent

Disinfection:

destroys most microbial life, reducing contamination on inanimate surfaces.

Virucide:

inactivates viruses, especially on living tissue

Fungicide:

kills fungal spores, hyphae, and yeasts

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 Sterilized products are essential to human well-being. Surgical instruments Syringes Commercially packaged foods

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

Irradiation:

Bombardment of microbes with radiation

Hypochlorites:

Broadly used in industry and allied health Household bleach is a weak solution of sodium hypochlorite

How antimicrobial agent works

Cellular targets of physical and chemical agents: The cell wall The cell membrane Cellular synthetic processes (DNA, RNA) Proteins

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

Fungistatic chemicals:

Inhibit fungal growth

Effects of UV radiation:

Initially absorbed by DNA Form pyrimidine dimers Abnormal linkages between adjacent pyrimidines (thymine and cytosine) Interfere with normal DNA replication and transcription Lead to inhibition of growth and death

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 water

Antisepsis:

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

Decontamination:

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

Filtration:

An effective method to remove microbes from air and liquids Fluid is strained through a filter with openings large enough for liquid to pass through, but too small for microbes to pass through Most filters are perforated by precise, uniform pores Coarse: 8 microns Ultrafine: 0.02 micron Allows selection of the minimum particle size to be trapped Even smaller pore diameters permit true sterilization by removing viruses and even large proteins

Tinctures:

Antimicrobial chemicals dissolved in pure alcohol or water-alcohol mixtures

Antispesis

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

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

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

Microbistatic agents:

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

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

Semicritical medical devices:

Come into contact with mucosal membranes

Iodophors:

Complex of iodine and alcohol Have replaced free iodine solutions in medical antisepsis

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

Effects of agents on 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

What is microbial death?

Death of microscopic organisms: 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

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.

Phenolics:

Destroy vegetative bacteria, fungi, and some viruses Able to act in the presence of organic matter Too toxic to use as antiseptics Phenolic derivatives combined with soap Bisphenols: Aerosol sprays and cleansing soaps Triclosan: Disinfectant and antiseptic chemical added to many products Chlorhexidine: Hand scrubbing, surgical prep, and other medical uses

Practical Concerns in Microbial Control

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?

Low-level germicides:

Eliminate only: Vegetative bacteria Vegetative fungal cells Some viruses Used to clean noncritical materials: Electrodes Straps Furniture that touches skin but not mucous membranes

Radiation:

Energy emitted from atomic activities and dispersed at high velocity through matter or space Radiation suitable for microbial control: Gamma rays X rays Ultraviolet radiation

Nonionizing radiation:

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

Critical medical devices:

Expected to come into contact with sterile tissues

Phenol:

First used as the major antimicrobial chemical Toxic and irritating side effects

Halogens

Fluorine, bromine, chlorine, iodine Microbicidal and sporicidal Active ingredients in ⅓ of all antimicrobial chemicals

Iodine and its compounds

Free iodine (I2) Iodophors All classes of organisms are killed by iodine if proper concentrations and exposure times are used Not adversely affected by organic matter

Chlorine and Its Compounds

Gaseous chlorine (Cl2) Hypochlorites (ClO1) Chloramines (NH2Cl) Kill bacteria, endospores, fungi, viruses Less effective if exposed to light, alkaline pH, and excess organic matter

Methods of physical control

Heat is the most widely used method of microbial control. Other methods: Radiation Filtration Ultrasonic waves Cold

Alcohols as Antimicrobial Agents

Only ethyl and isopropyl alcohol are appropriate for microbial control. Greater efficacy at 70% Destroys vegetative microbial forms but not endospores. More effective against enveloped viruses than non-enveloped viruses

Antisepsis/degermation: (decontamination)

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

Historical microbial control methods:

Salting food Smoking food Pickling food Drying food Exposing food, clothing, and bedding to sunlight

Decontamination

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

Antimicrobial chemicals

Solid Liquid Gaseous For convenience, solid or gaseous antimicrobial chemicals are dissolved in water, alcohol, or a mixture of the two

Aseptic techniques:

Sterile methods that exclude all microbes

Four possible outcomes of microbial control outside the body:

Sterilization Disinfection Antisepsis Decontamination

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

Thermal death point:

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

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

Aqueous iodine:

Topical antiseptic, treatment for burned skin00

Chloramines:

Used as alternatives to pure chlorine in water treatment

Iodine tablets:

Used for disinfecting water

Applications of filtration

Used in liquids that cannot withstand heat. Alternative method for decontaminating milk and beer. Important step in water purification. Efficient means of removing airborne contaminants.

Iodine tincture:

Used in skin antisepsis

Sporicide:

capable of killing endospores

Germicide and microbicide:

chemical agents that kill microorganisms

Sterilization:

the destruction of all microbial life.

Factors Affecting the Microbicidal Activity of Chemicals

Nature of microorganisms being treated Nature of material being treated Degree of contamination Time of exposure Strength and chemical action of the germicide

Factors that effect death rates

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

Cold sterilization:

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

High-level germicides:

Kill endospores Sterilants if properly used Critical items that are not heat-sterilizable Catheters Heart-lung equipment

Intermediate-level germicides:

Kill fungal but not bacterial spores, resistant pathogens such as the tubercle bacillus, and viruses Used to disinfect semi-critical items: Respiratory equipment Thermometers

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

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