Controlling Microbial Growth in the Environment

Sterilization

The removal or destruction of all microbes, including viruses and bacterial endospores, in or on an object.

Aseptic

An environment or procedure that is free of contamination by pathogens.

Disinfection

The use of physical or chemical agents known as disinfectants to inhibit or destroy microorganisms, especially pathogens.

Antisepsis

The process of using a chemical on skin or other tissue.

Degerming

The removal of microbes from a surface by scrubbing, such as when you wash your hands.

Sanitization

The process of disinfecting places and utensils used by the public to reduce the number of pathogenic microbes to meet acceptable public health standards.

Pasteurization

The use of heat to kill pathogens and reduce the number of spoilage microorganisms in food and beverages.

Bacteriostatic

Agents or techniques that inhibit the growth of microbes without necessarily killing them.

Cidal

Words ending in -cide or -cidal refer to agents or methods that destroy or permanently inactivate a particular type of microbe.

Microbial Death

The permanent loss of reproductive ability under ideal environmental conditions.

Microbial Death Rate

A constant rate of microbial death found over time for any particular microorganism under a particular set of conditions.

Semilogarithmic Graph

A graph where the microbial death rate plotted produces a straight line.

Modes of Action of Antimicrobial Agents

Physical or chemical agents may disrupt the integrity of cells by altering their cell walls or cytoplasmic membranes.

Cell Wall Disruption

Makes the cell susceptible to osmotic lysis.

Cellular Metabolism Interruption

Chemical or physical agents interrupt cellular metabolism and reproduction by interfering with the structures of proteins and nucleic acids.

Osmotic Lysis

The rupture of a cell due to the influx of water when the cell wall is disrupted.

Innocuous Microbes

Microbes that may still be present after sterilization techniques eradicate harmful microbes.

Disinfectants

Physical or chemical agents used in disinfection to inhibit or destroy microorganisms.

Antiseptics

Agents used in antisepsis on skin or other tissue.

Public Health Standards

The acceptable number of pathogenic microbes in places and utensils used by the public.

Spoilage Microorganisms

Microorganisms that can cause spoilage in food and beverages, which are reduced by pasteurization.

Chemical Agents

Substances that can disrupt cellular integrity or metabolism.

Physical Agents

Methods that can disrupt the integrity of microbial cells.

Cytoplasmic membrane

Contains the cell contents and controls what enters and leaves the cell.

Envelope of enveloped viruses

Important for attachment, and damage to it can prevent infection.

Denatured protein

A protein that has lost its correct shape due to broken hydrogen and sulfide bonds.

Factors affecting antimicrobial methods

The nature of the sites to be treated, the degree of susceptibility of microbes involved, and the environmental conditions.

Site to be treated

Influences the choice of antimicrobial method

Relative susceptibility of microorganisms

Methods are selected to kill the hardiest microorganisms present, assuming more fragile microbes will be killed as well.

Bacterial endospores

The most resilient forms of life.

Mycobacterium

Species resistant to drying and many chemical disinfectants due to their waxy cell walls.

Cyst wall of protozoa

Protects the organisms from the action of disinfectants and some physical methods.

Prions

Infectious proteins that are more resistant than any living thing.

Effectiveness of germicides

Classified as high, intermediate, and low based on their ability to inactivate or destroy microorganisms.

Environmental conditions

Conditions such as temperature and pH that affect the efficacy of disinfectants.

Biosafety Levels

Guidelines for four levels of safety in microbiological laboratories established by the CDC.

BSL-1

Suitable for nonpathogenic microbes.

BSL-2

Intended for moderately hazardous microbes.

BSL-3

Designed for containment of true pathogens, includes specifications for the physical facility and procedures.

BSL-4

Designed for the most dangerous pathogens with stringent guidelines for facility design.

Physical methods of microbial control

Include exposing microbes to extremes of heat and cold, desiccation, filtration, osmotic pressure, and radiation.

Heat-related methods

Use high temperatures to denature proteins, interfere with cytoplasmic membranes and cell walls, and disrupt nucleic acids.

Microorganisms' susceptibility to heat

Microorganisms vary in their susceptibility to heat.

Thermal death point

The lowest temperature that kills all cells in a broth in 10 minutes.

Thermal death time

The time it takes to completely sterilize a particular volume of liquid at a set temperature.

Decimal reduction time (D)

The time required to destroy 90% of the microbes in a sample.

D value for C. botulism endospores at 121°C

0.204 minutes.

Moist heat

More effective than dry heat because water is a better conductor of heat than air.

Boiling

Kills the vegetative cells of bacteria and fungi, the trophozoites of protozoa, and most viruses within 10 minutes at sea level.

Autoclaving

A method required to achieve true sterilization using moist heat.

Autoclave

A device consisting of a pressure chamber, pipes, valves, and gauges that uses steam heat under pressure to sterilize chemicals and objects that can tolerate moist heat.

Temperature for autoclaving

121°C for 15 minutes is sufficient to kill all microbes in small volumes.

Bacterial endospores

Used as indicators of sterility.

Pasteurization

A method of heating foods to kill pathogens and control spoilage organisms without altering the quality of the food.

Historical pasteurization method

At 63°C for 30 minutes.

Flash pasteurization

At 72°C for 15 seconds.

Ultrahigh-temperature pasteurization

At 135°C for 1 second.

Ultrahigh-temperature sterilization

Makes use of steam at 140°C for 1 to 3 seconds to sterilize liquids and foods.

Dry heat

Used to sterilize substances that cannot be sterilized by moist heat, such as powders and oils.

Complete incineration

The ultimate means of sterilization.

Refrigeration temperature range

Between 0°C and 7°C halts the growth of most pathogens.

Notable exception to refrigeration

Listeria.

Slow freezing

Effective in inhibiting microbial metabolism at temperatures below 0°C.

Desiccation

The process of drying that inhibits microbial growth because metabolism requires liquid water.

Lyophilization

A process that preserves microbes and other cells for many years by freeze-drying.

Sublimation

The process where frozen water subjected to a vacuum is transformed directly from a solid to a gas.

Filtration

The passage of air or a liquid through a material that traps and removes microbes.

HEPA filters

Remove microbes and particles from air.

Osmotic pressure

High concentrations of salt or sugar inhibit microbial growth by drawing the water out of cells.

Examples of foods preserved by osmotic pressure

Honey, jams, salted fish, and pickles.

Fungi tolerance to hypertonic environments

Fungi have a greater tolerance for hypertonic environments than bacteria.

Particulate radiation

Consists of high-speed subatomic particles freed from their atoms.

Electromagnetic radiation

Atomic energy without mass traveling at the speed of light.

Ionizing radiation

Electromagnetic radiation with wavelengths shorter than 1 nm, such as electron beams, gamma rays, and some X rays.

Nonionizing radiation

Radiation with wavelengths longer than 1 nm, including ultraviolet light, visible light, infrared light, and radio waves.

Ultraviolet light

A type of nonionizing radiation that has sufficient energy to be a practical antimicrobial agent.

Pyrimidine dimers

DNA damage caused by ultraviolet light that can kill affected cells.

Phenol and Phenolics

Compounds derived from phenol molecules that have been chemically modified and are effective disinfectants.

Bisphenolics

Composed of two covalently bonded phenolics, such as triclosan.

Alcohols

Chemicals like isopropanol that denature proteins and disrupt cytoplasmic membranes.

Tincture

A combination of an alcohol and another antimicrobial chemical.

Halogens

Reactive nonmetallic elements including iodine, chlorine, bromine, and fluorine, used as antimicrobial chemicals.

Iodophor

A compound that releases iodine slowly, used medically.

Oxidizing Agents

High-level disinfectants like hydrogen peroxide, ozone, and peracetic acid that release oxygen radicals.

Hydrogen peroxide

An oxidizing agent that can disinfect and sterilize surfaces but is not useful in treating open wounds.

Surfactants

Surface active chemicals including soaps and detergents that disrupt cellular membranes.

Quaternary ammonium compounds (quats)

A type of surfactant considered low-level disinfectants, ineffective against certain pathogens.

Heavy Metals

Metals used in microbial control, though the specific details are not provided in the notes.

Bactericidal

Refers to substances that kill bacteria.

Fungicidal

Refers to substances that kill fungi.

Virucidal

Refers to substances that kill viruses, specifically enveloped viruses.

Intermediate-level disinfectants

Disinfectants that are effective against a broad range of pathogens but not all.

Sporicide

A chemical agent that can kill bacterial spores.

Heavy metal ions

Low-level disinfectants that denature proteins, including arsenic, silver, mercury, copper, and zinc.

Silver

An antimicrobial agent used in some surgical dressings, burn creams, and catheters.

Copper

An effective algicide used to inhibit the growth of mold.

Aldehydes

Compounds containing terminal -CHO groups that cross-link organic functional groups in proteins and DNA.

Glutaraldehyde

A 2% solution that is an effective disinfectant.

Formaldehyde

A 37% aqueous solution used to disinfect or sterilize equipment and in embalming fluid.

Gaseous Agents

Highly reactive gases such as ethylene oxide, propylene oxide, and beta-propiolactone that denature proteins and DNA.