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Sterilization Definition

Sterilization is used in healthcare institutions to eradicate or destroy all forms of microbial life, including fungi, bacteria, multicellular eukaryotic organisms, and other biological agents.

Sterilization Definition

Sterilization is carried out to stop the growth of microbes that may colonize an object's surface if the germs are not eradicated. Heat, sunlight, high pressure, radiation, filtration, & chemicals are just a few sterilization methods. Disinfection, sanitization, & pasteurization are different from sterilization in that they lessen rather than eliminate any living organisms or biological agents that could be present. A thing that has been sterilized is referred to as sterile or aseptic.

Classification of Sterilization

In microbiology, sterilization can be accomplished using various physical and chemical techniques. Physical sterilization & chemical sterilization are the two categories under which sterilization is categorized. Let's go through them in more depth.

Physical Sterilization Methods

The following methods are included in physical sterilization:

Sterilization Definition

Heat Sterilization

Heat sterilization is the most effective method of sterilization since it completely gets rid of bacteria by destroying their enzymes and cellular components. It is done using two techniques:

1. Wet Heat- It is one of the best sterilizing methods. An autoclave is used to carry out the moist heat sterilization process. Pressure-driven steam generation is the principle underlying how an autoclave works. Therefore, steam sterilization is another name for wet heat sterilization. Steam is often used in wet heat sterilization at temperatures between 121 to 134 °C.

High pressure raises the boiling point of water, allowing for a greater temperature for sterilization.

This approach is far more efficient than dry heat sterilization, which kills bacteria by oxidation. In this process, the microorganisms are destroyed by coagulating their proteins. It is used in the medical and pharmaceutical sectors to treat dirty and contaminated products and sterilize bandages, sheets, surgical & diagnostic types of equipment, containers, and more.

2. Dry Heat- It should be obvious from the name that the dry heat method doesn't need any water; hence hydrolysis won't occur here. The two best practices for using dry heat are flaming and baking. The oxidation of biological components kills bacteria using dry heat procedures. The material is heated since it takes more effort and energy than just breaking down proteins. When an autoclave is used, sterilization can be completed in about 15 minutes. However, dry heating necessitates sterilizing the item to 160 degrees Celsius. It's one of the most trustworthy sterilization procedures that is frequently used in sterilizing methods. The micro lab doesn't need a specialist to carry out this heating because it is the simplest method.

Dry heat sterilization comes in a variety of forms, which are described below:

Red Heat-

  • The procedure of red heat sterilization involves keeping the equipment in a Bunsen flame until they are red-hot to sterilize them instantly.
  • This dry heat sterilization procedure is often used for sterilizing devices such as incubator loops, wires, and forceps tips.
  • This method guarantees efficient sterilization but can only be used on materials that can withstand heating until they become red under the flame.


  • Flaming is a sort of dry sterilization where metallic items are exposed to flame for some time, causing the flame to burn any dust or other contaminants present in the instrument.
  • Flaming is dipping an instrument in alcohol/spirit and then burning it over a gas flame.
  • This method is less efficient than red-hot sterilizing and does not guarantee sterility.


  • Sterilization and a large waste volume reduction are achieved via incinerating trash. Usually, it takes place at the hospital or any other leftovers' final disposal.
  • The leftovers are heated until they turn to ash, which is subsequently thrown away.
  • An incinerator is the equipment used for this operation.

Hot air oven-

  • Dry heat sterilization with a hot air oven allows for sterilizing items that cannot be sterilized using moist heat.
  • It operates on conduction, whereby the outside surface absorbs heat before transmitting it to the internal part.
  • An insulated chamber with a fan, thermocouples, a temperature sensor, shelves, and door-locking controls make up a hot air oven.

Infrared radiation-

  • A technique for thermal sterilization known as infrared radiation (IR) involves absorbing the radiation and converting it to heat energy.
  • A tunnel with Infrared radiation is used for this. The trays containing the sterilized glassware and tools are transported through the tunnel at a predetermined speed.
  • Syringes and packaged catheters can be sterilized in bulk using IR.


Filtration is distinct from other sterilizing methods in that it eliminates bacteria rather than removing them. However, cleaning the liquid takes more time. It may also clarify and sterilize liquids and gases since it can block the flow of both viable & nonviable particles. For the filtering procedure, there are several types of filters available. The most common filter types are

  • Candle filter- This new mechanical filter is comprised of diatomous mud. Small holes on it have the propensity to absorb microorganisms. Microbes become trapped in the candle filters' pores when the fluid goes through them.
  • Membrane Filter- Cellulose is used to create the membrane filters. While sterilizing the material, the membrane must be positioned between the needle and syringe. The sterilizing of gases, solvents, and fluids can be accomplished using this filter.
  • Seitz filter- Since Seitz filters are formed of asbestos, they have a robust construction and can filter solutions. The Seitz filter absorbs the solution as it goes through, leaving microorganisms & residues on the filter's top.
  • Sintered glass filter- Filters constructed of sintered glass don't absorb liquids during filtering since they are composed of glass. The biggest disadvantage of this approach is the filter's fragility and propensity to break quickly.


To sterilize surfaces and things, the process of irradiation involves exposing them to various radiation types. For sterilizing, electromagnetic radiation is mostly used.

  • Ultraviolet radiation (non-ionizing)

Due to the low energy and low penetrating capacity of non-ionizing rays, UV rays have a wavelength between 260 and 280 nanometers. They are exposed to the material intoet rid of germs and other microbes.

UV radiation is inappropriate for sterilizing pharmaceutical dosage forms due to its weak capacity to penetrate traditional packaging materials.

Nevertheless, it is used to treat manufacturing-grade water, sterilize air, and sterilize the surfaces of aseptic work environments.

  • Ionizing Radiation

The two types of ionizing radiation most frequently used for sterilization are X and gamma rays. These are highly energetic radiations that ionize different substances, including water.

A significant number of hazardous O2 metabolites, including the hydroxyl radical, superoxide ions, and H2O2, are produced through the ionization of water. These metabolites are strong oxidizers that destroy bacteria by different oxidizing parts of their cells.

  • Electromagnetic Radiation

High-speed electrons are accelerated in this technique using the cathode material. The electromagnetic beams are created to eliminate all types of bacteria, fungi, viruses, and other microorganisms. Cold sterilization is the term used to describe this method of eradicating microorganisms via radiation.

Sunlight (Solar Disinfection)

  • With sunshine, the solar disinfection method is performed to get rid of bacteria. Drinking water is frequently cleaned or disinfected using this method.
  • The UV-A portion of sunlight, which combines with water's dissolved oxygen to release reactive forms of oxygen, is what causes pathogenic organisms to become inactive during solar disinfection.
  • Pathogens are damaged by these compounds, disrupting metabolism and breaking down bacterial cell walls while simultaneously heating the surface with the complete spectrum of solar radiation (from infrared to UV).
  • The idea behind sun disinfection is similar to radiation sterilization; however, its effectiveness is considerably lower due to the lengthy exposure time.

Chemical Sterilization Method

Sterilization Definition

Chemicals are the everyday substances in a microbiology laboratory. While some chemicals have potentially harmful side effects, they work remarkably well to eradicate several unseen microorganisms. Chemical approaches have gained popularity since they are simple and cost-effective. Chemicals can eliminate harmful microorganisms from the surface by acting as disinfectants.

Modern tools and devices used in hospitals and laboratories, like a a custom trayare frequently heat-sensitive. This indicates that they include some parts that should be protected from high temperatures. These components include rubber, glass, plastic, and other substances of the same kind. The option suggested is chemical sterilization, which may sterilize them without needing heat. Chemical sterilization can be done using liquid or gaseous chemicals.

  • Liquid- The act of immersing an object in a liquid to kill all living germs and their spores is known as liquid sterilization. This technique, which is used to get rid of low levels of contamination, is less efficient than gaseous sterilization.
  • Aldehydes- A 40% formaldehyde solution is used to disinfect surfaces. Some of the finest aldehydes used in this method include formaldehyde and glutaraldehyde. 50% phenol can also be used.
  • Heavy Metals- Some heavy metals and chemicals can sterilize objects. The sterilizing process uses heavy metals such as copper sulfate, mercuric salts, mercuric chloride, and silver nitrate mercuric chloride. Similarly, bacterial nucleic acids can be affected by dyes like aminacrine, acridine, & acriflavine.
  • Gaseous- The process of gaseous sterilization involves exposing the object to gas in a confined, heated, and pressurized chamber. Gases that can effectively destroy bacterial spores include formaldehyde and ethylene oxide.

It is possible to sterilize instruments chemically without heating them. But not all equipment and devices can be disinfected using this technique because some equipment or instruments include components that may react strongly with chemicals. It is advised that you read the manufacturer's instructions from the makers of the chemicals and the equipment to be sterilized before utilizing a chemical sterilization technique with these kinds of devices.

Advantages and Disadvantages of Sterilization


  • Prevent Disease Transmission.
  • Prevent contamination
  • Prominent growth of harmful bacteria.
  • Preventing material degradation caused by bacteria


  • The cost is really expensive.
  • High probability of accidents
  • Risk of skin burning
  • Difficult to handle
  • Chances of causing respiratory disease at the time of operation.

The Conclusion

Sterilization is an essential procedure. It has a significant role in surgical management's success. However, alternative techniques are also employed for heat-sensitive products. Overall, heat sterilization is the best way. Boiling destroys the majority of vegetative cells but not bacterial spores. In comparison to moist heat, dry heat takes longer to kill organisms.

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