What is sterilization and what are the main processes by which pathogens can be completely eliminated?
Decontamination is an essential aspect in the medical field and beyond. The two types of decontamination are sterilization and disinfection. Eliminating pathogens is essential for preventing infections. Cleaning is not the same as decontamination. While cleaning can remove dirt and dust, decontamination involves the neutralization or removal of hazardous substances, radioactivity, or germs from an area, object, or person, and is achieved through sterilization.
Table of Contents
- What is sterilization?
- The difference between sterilization, disinfection, and cleaning
- Different sterilization methods used in the laboratory
1. What is sterilization?
Sterilization can be defined as the process of statistically complete elimination of all microorganisms, including the most resistant bacteria and spores. It is a difficult condition to achieve and prove. Although there are many chemical, inorganic, and organic substances that kill microorganisms, they may not be completely effective and may leave behind unwanted or toxic residues.
Sterilization and disinfection are the core components of hospital infection control activities. Every day, numerous surgical procedures are performed in a hospital. The medical device or surgical instrument that comes into contact with sterile tissue or the patient's mucous membrane during various processes is associated with an increased risk of introducing pathogens into the patient's body.
Moreover, there is a possibility of infection transmission from patient to patient; from patient to healthcare personnel and vice versa; or from the environment to the patient through improperly sterilized or disinfected devices. Therefore, medical staff, laboratory personnel, and healthcare providers should have better knowledge regarding sterilization and disinfection techniques to prevent the spread of these pathogens.
2. The difference between sterilization, disinfection, and cleaning
Sterilization describes a process that destroys or eliminates all forms of microbial life and is performed in healthcare facilities through physical or chemical methods. Pressurized steam, dry heat, EtO gas, hydrogen peroxide gas plasma, and liquid chemicals are the main sterilizing agents used in healthcare facilities.
Sterilization
Sterilization is intended to convey an absolute meaning; unfortunately, however, some healthcare professionals and technical/commercial literature refer to "disinfection" as "sterilization" and to items as "partially sterile." When chemicals are used to destroy all forms of microbiological life, they can be called chemical sterilants. The same germicides used for shorter exposure periods can also be part of the disinfection process (e.g., high-level disinfection). (Source)
Disinfection
Disinfection describes a process that eliminates many or all pathogenic microorganisms, except for bacterial spores, from inanimate objects. In healthcare settings, objects are usually disinfected via liquid chemicals or wet pasteurization. Any of the various factors that affect the efficacy of disinfection can negate or limit the effectiveness of the process.
Factors that influence the efficacy of both disinfection and sterilization include pre-cleaning of the object; the organic and inorganic load present; the type and level of microbial contamination; the concentration of and exposure time to the germicide; the physical nature of the object (e.g., crevices, hinges, and lumens); the presence of biofilms; the temperature and pH of the disinfection process; and, in some cases, the relative humidity of the sterilization process (e.g., ethylene oxide).
Unlike sterilization, disinfection is not sporicidal. Certain disinfectants will destroy spores with prolonged exposure times; these are called chemical sterilants. At similar concentrations, but with shorter exposure periods (e.g., 20 minutes for 2% glutaraldehyde), the same disinfectants will kill all microorganisms except for a large number of bacterial spores; these are called high-level disinfectants.
Cleaning represents the removal of visible dirt (e.g., organic and inorganic materials) from objects and surfaces and is normally performed manually or mechanically using water with detergents or enzymatic products.
Cleaning
Thorough cleaning is essential before high-level disinfection and sterilization because inorganic and organic materials remaining on instrument surfaces interfere with the efficacy of these processes. Decontamination removes pathogenic microorganisms from objects so that they can be handled, used, or discarded safely.
Terms with the suffix "-cide" or "-cidal" for killing action are also commonly used. For example, a germicide is an agent that can kill microorganisms, especially pathogenic organisms ("germs"). The term germicide includes both antiseptics and disinfectants.
Antiseptics are germicides applied to living tissue and skin; disinfectants are antimicrobials applied only to inanimate objects. In general, antiseptics are used only on the skin and not for surface disinfection, and disinfectants are not used for skin antisepsis because they can damage the skin and other tissues. Virucide, fungicide, bactericide, sporicide, and tuberculocide can kill the type of microorganism identified by the prefix. For example, a bactericide is an agent that kills bacteria. (Source)
Klintensiv Tip: Choosing the right products for disinfection, sterilization, and cleaning is essential. Also, for hygiene in sanitary spaces, we recommend only using professional products specifically designed for the healthcare field.
3. Different sterilization methods used in the laboratory
In laboratory settings, the importance of sterilization cannot be overstated. Sterilization is the process of eliminating or destroying all forms of microbial life, including bacteria, viruses, spores, and fungi, from a surface or environment. Sterilization methods in the laboratory are essential for ensuring the accuracy and reliability of experiments, as well as for maintaining a safe working environment.
Laboratory sterilization can be achieved through a combination of heat, chemicals, irradiation, high pressure, and filtration, such as pressurized steam, dry heat, ultraviolet radiation, gas vapor sterilizers, chlorine dioxide gas, etc. Effective sterilization techniques are essential for working in a laboratory, and neglecting them could lead to serious consequences, potentially costing a life.
So, what are the most frequently used sterilization methods in the laboratory and how do they work?
Sterilization by heat
This is the most common method of sterilization. Heat is used to kill microbes. The degree of sterilization is affected by the temperature of the heat and the duration of heating. Based on the type of heat used, heat methods are classified into:
- Moist heat/steam sterilization. In most laboratories, this is a widely used method performed in autoclaves. Autoclaves use steam heated to 121-134 °C under pressure. This is a very effective method that kills/deactivates all microbes, bacterial spores, and viruses. Autoclaving kills microbes through the hydrolysis and coagulation of cellular proteins, which is efficiently achieved by intense heat in the presence of water.
- Dry heat sterilization. In this method, test tubes containing bacteria are exposed to high temperatures either by flame, incineration, or a hot air oven. Flame is used for metal devices such as needles, scalpels, scissors, etc. Incineration is especially used for inoculation loops used in microbe cultures. The metal end of the loop is heated until red-hot.
Filtration
Filtration is the fastest way to sterilize solutions without heating them. This method involves filtering with a pore size too small for microbes to pass through. Generally, filters with a pore diameter of 0.2 μm are used for eliminating bacteria. Membrane filters are used more frequently than sintered filters or Seitz or candle filters. It should be noted that viruses and phages are much smaller than bacteria, so the filtration method is not applicable if these are the primary concern.
In this sterilization method, three types of filters are used:
- Seitz filters: Constructed from materials such as asbestos, these filters are pad-type and are thicker than membrane filters. Seitz filters remain intact during filtration but can absorb the solution. Sintered glass filters serve as an alternative; made of glass, they do not absorb liquids but are delicate and prone to breaking.
- Membrane filters: These thin filters, made of cellulose, are suitable for real-time sterilization during injections. Positioned between the needle and syringe, these filters are nonetheless susceptible to breaking, which can compromise the sterilization process.
- Candle filters: Composed of clay materials, such as diatomaceous earth, these filters contain tiny pores created by algae. The filters feature numerous elongated pores that trap microbes as they navigate through the candle.
Sterilization by radiation
This method involves exposing packaged materials to radiation (UV, X-rays, gamma rays) for sterilization. The main difference between the various types of radiation is their penetration and, therefore, their efficacy. UV rays have low penetration and are therefore less effective, but they are relatively safe and can be used for small surface sterilization. X-rays and gamma rays have a much higher penetration power and are therefore more effective for large-scale sterilization. However, it is more dangerous and therefore requires special attention.
UV irradiation is commonly used to sterilize the interior of biological safety cabinets between uses. X-rays are used for sterilizing large packaging and pallets of medical devices. Gamma radiation is commonly used for sterilizing disposable medical equipment, such as syringes, needles, cannulas, and IV sets, as well as food.
Chemical sterilization
Heating offers a reliable way to get rid of all microbes, but it is not always suitable because it can damage the material that needs to be sterilized. In this case, chemical sterilization methods are used, which involve the use of liquids and gases without affecting the material. Sterilization is effective with the help of gases because they penetrate the material rapidly, much like steam.
The gases commonly used for sterilization are a combination of ethylene oxide and carbon dioxide. Carbon dioxide is added here to minimize the chances of an explosion. Ozone gas is another option that oxidizes most organic matter. Hydrogen peroxide, nitrogen dioxide, glutaraldehyde and formaldehyde solutions, phthalaldehyde, and peracetic acid are other examples of chemicals used for sterilization.
Solvent sterilization
In the solvent sterilization method, isopropanol is most frequently used as a solvent for fats, while ethanol is usually used as a disinfectant. Both denature proteins through a process involving water. What is important to remember here is that while ethanol and isopropanol effectively kill microbial cells, they do not have the same effect on spores.
Conclusion
Understanding the different sterilization methods and their specific applications is essential for hospital professionals to maintain a sterile environment. The choice of sterilization method depends on factors such as material composition, sensitivity to temperature, and the presence of organic matter. By staying informed about these techniques, medical and sterilization staff can optimize their sterilization processes and promote a safe and reliable working environment.
Sources:
https://www.westlab.com/blog/different-sterilization-methods-used-in-the-laboratory
https://www.westlab.com/blog/different-sterilization-methods-used-in-the-laboratory
