(Latin sterilis – unable to produce offspring or barren) is the process by which all living cells, viable spores, viruses, and viroids are either destroyed or removed from an object or habitat, and achieved by physical means and chemical means
Sterilant
A chemical agent used to achieve sterilization
Disinfection
The killing, inhibition, or removal of microorganisms that may cause disease; the primary goal is to destroy potential pathogens, but disinfection substantially reduces the total microbial population
Disinfectants
Agents, usually chemical, used to carry out disinfection and are normally used only on inanimate objects
Germicide
A suffix can be employed to denote the type of antimicrobial agent. Substances that can kill organisms often have the suffix – cide (Latin cida, to kill) kill pathogens (and many non-pathogens) but not necessarily endospores
A larger population
Requires a longer time to die than a smaller one
Conditions influencing the effectiveness of antimicrobial agent activity
Population Composition
Concentration or Intensity of an Antimicrobial Agent
Duration of Exposure
Temperature
Local Environment
Heating
Fire and boiling water have been used for sterilization and disinfection since the time of the Greeks, and heating is still one of the most popular ways to destroy microorganisms
Types of heat
Moist Heat
Dry Heat
Moist Heat - Temperature below 100-degree Celsius
Pasteurization
Vaccine Bath
Serum Bath
Inspissation
Pasteurization
Many substances, such as milk, are treated with controlled heating at temperatures well below boiling point. (developed by Louis Pasteur)
Types of Pasteurization
Flash pasteurization / high temperature short term (HTST) pasteurization
Ultrahigh-temperature (UHT) sterilization
Flash pasteurization / high temperature short term (HTST) pasteurization
Quick heating to about 72 degree C for 15 seconds, then rapid cooling
Ultrahigh-temperature (UHT) sterilization
Heated 140 to 150 degrees C for 1 to 3 seconds; does not require refrigeration, (room temperature) for about 2 months without flavor changes
Vaccine Bath
This is used to destroy contaminating bacteria in vaccine preparations; heated in a water bath at 60 ° C for one hour daily in a vaccine bath for several successive days; only vegetative forms of the bacteria are destroyed
Serum Bath
Used to inactivate bacteria contaminating serum preparations; heating at 56°C for several successive days; similar to vaccine bath, only the vegetative forms are destroyed since higher temperatures will cause coagulation of proteins present in the serum
Inspissation
Used to solidify and disinfect egg-containing and serum-containing bacteria; heated at 80°C -85°C for 30 minutes for three successive days
Moist Heat - Temperature at 100-degree Celsius
Boiling
Fractional Sterilization (Tyndallization)
Boiling
Involves utilizing water at a boiling temperature of 100°C; it is not sporicidal; only destroys vegetative forms; certain metal articles and glassware can be disinfected using this method for 10-20 minutes without opening the lid of the boiler
Fractional Sterilization (Tyndallization)
Intermittent sterilization; live steam at 100°C for 30-90 minutes for three consecutive days (depending on the material to be sterilized); sterilized culture media and selenite broth
Moist Heat - Temperature above 100-degree Celsius
Steam Sterilization
Steam Sterilization
Moist heat sterilization must be carried out at temperatures 100 degrees C to destroy bacterial endospores, and this requires the use of saturated steam under pressure; steam sterilization is carried out with an autoclave, a device somewhat like a fancy pressure cooker; usually, 121 degrees C and 15 pounds of pressure
Dry Heat
Open Flame
Red Flame
Incineration
Hot Air Oven
Infrared Rays
Desiccation
Freezing
Filtration
Radiation
Sonic and Ultrasonic Vibrations
Osmotic Pressure
Red Flame
This method is used to sterilize articles like bacteriological wire loops, straight wires, tips of forceps, and searing spatulas; the materials are held over the flame of a Bunsen burner until they become red-hot
Open Flame
Also makes use of the Bunsen burner or alcohol lamp; material sterilized is passed over the flame several times but is not heated to redness; aimed at burning the organism into ashes and is used to sterilize articles as mouths of test tubes, scalpels, glass slides, and cover slips; cracking of the glassware may occur
Incineration
Aimed at burning the organism into ashes; the contaminated material is burned using an incinerator; articles incinerated include soiled dressings and beddings, animal carcasses, and pathological material; used only for articles that have to be disposed
Hot Air Oven
Introduced by Louis Pasteur; articles are placed in the oven at a temperature of 160°C for one hour; it can be used to sterilize certain glassware (e.g., Petri dishes, pipettes, and flasks); and the only method used to sterilize powders and ointments; disadvantages: poor conductor of heat; wool and paper slightly charred and glasses can become smoky
Infrared Rays
Articles to be sterilized are placed in a conveyor belt and passed through a tunnel that is heated by infrared radiators; the temperature is 180 °C for 7.5 minutes; sterilize metallic equipment and glassware
Desiccation
This method is based on the principle of depriving the microorganisms of moisture; it is used mainly for food preservation, such as in the preparation of dried fish and fruits; it destroys vegetative forms; endospores are resistant to drying
Freezing
Inhibits microbial growth and reproduction by low temperature and absence of liquid water
Filtration
Removes contaminating microorganisms without directly destroying them; sterilizes heat-sensitive materials
HEPA Filters (Air)
Used in operating rooms and burn units to remove bacteria from the air
Membrane Filters (Liquids)
Porous membranes made of various synthetic materials, replace depth filters for many purposes
Ultraviolet Light (UVL) / Non-ionizing Radiation
Effective wavelength is 200 nm - 280 nm, with 260 nm as the most effective; can inactivate microorganisms like bacteria, viruses, and yeasts within seconds
Ionizing Radiation
Greater penetrance than UV rays; causes formation of free radicals that chemically interact with proteins and nucleic acids, resulting in cell death
Electron Beams
Generated by a linear accelerator, can be used to sterilize various items
Electromagnetic (Gamma Rays)
Greater penetrance than electron beams but requires longer exposure time
SonicandUltrasonicVibrations
Can kill some bacteria and viruses after exposure to certain frequencies
Osmotic Pressure
Based on the principle of Osmosis; creating a hypertonic environment (high concentration of salts and sugar)
Surface Active Agents (Surfactants)
Long-chain hydrocarbons that are fat-soluble and charged ions that are water-soluble