Disinfection and sterilization constitute a crucial step in preventing and controlling contamination in microbiological laboratories. All instruments and utensils used in the laboratory must undergo strict disinfection and sterilization processes. Common equipment typically includes glassware, metal instruments, rubber products, and plastic products, among others. Different disinfection and sterilization methods are applied to each category of equipment.
I. Concepts
Disinfection refers to the process of killing or removing pathogenic microorganisms on a transmission medium to render them harmless. It can be divided into preventive disinfection and epidemic-source disinfection based on the presence or absence of a known source of infection.
Sterilization refers to the process of killing or removing all microorganisms (including spores) on a transmission medium to achieve a sterile state. Items that have undergone sterilization are called “sterile items”.
II. Disinfection and sterilization methods
At present, the commonly used disinfection and sterilization methods are mainly divided into two major categories: physical methods and chemical methods.
Physical methods:
- Dry heat sterilization
1.1 Hot air sterilization
Hot air sterilization achieves high-temperature sterilization using a constant-temperature drying oven. Due to the poor thermal penetration of dry heat and the strong heat resistance of microorganisms, prolonged exposure to high temperatures is necessary to achieve sterilization. Therefore, the temperature used in hot air sterilization is generally higher than that in moist heat sterilization.
To ensure sterilization effectiveness, the following parameters are typically specified. This method kills bacteria and bacterial spores to achieve sterilization:
Sterilization at 135-140°C for 3-5 hours;
Sterilization at 160-170°C for 2-4 hours;
Sterilization at 180-200°C for 0.5-1 hour.
It is mainly suitable for the sterilization of glassware, metal instruments that are inconvenient to be sterilized in a pressure steam sterilizer and not easily damaged by high temperatures, as well as items that cannot come into contact with steam.
1.2 Flame Incineration Method
Principle: The items to be sterilized are burned in a flame, which carbonizes all living organisms. This method is simple and thorough but causes significant damage to the items.
Applicable to: Sterilization of items with no economic value and experimental tools that are not susceptible to damage from burning, such as inoculating loops, forceps, test tubes, and blades.
- Moist Heat Sterilization
Moist heat sterilization using pressurized steam is currently one of the most commonly used sterilization methods. It utilizes high-pressure steam, along with the latent heat effect and excellent penetration capability present in the steam environment, to cause the coagulation and denaturation of bacterial proteins, thereby killing microorganisms.
It is suitable for the sterilization of cloth work clothes, various utensils, metal instruments, rubber stoppers, distilled water, cotton plugs, paper, and certain culture media.
- Radiation sterilization method
It is a sterilization method that uses an ultraviolet (UV) lamp for irradiation. Ultraviolet rays are a type of low-energy electromagnetic radiation capable of killing a variety of microorganisms. The mechanism of action of ultraviolet rays involves inactivating microorganisms by damaging their nucleic acids, proteins, and other components.
It is suitable for disinfecting clean benches, biosafety cabinets, and entire laboratory rooms.
- Filtration sterilization method
It is a method that removes microorganisms from gases or liquids based on the principle that bacteria cannot pass through dense, porous filter materials. It is often used for sterilizing heat-labile pharmaceutical solutions or raw materials.
It is suitable for reagents, enzyme solutions, sera, culture media, and other substances that are prone to decomposition, denaturation, and loss of efficacy when exposed to heat.
Chemical methods:
- Chemical disinfectant sterilization method
Commonly used chemical disinfectants include formaldehyde, potassium permanganate, 70%-75% ethanol, peracetic acid, hydrogen peroxide, 0.1% benzalkonium bromide, ethylene oxide, povidone-iodine, or tincture of iodine.
It is suitable for items that cannot be sterilized by physical methods, as well as air, work surfaces, operators’ skin, and certain laboratory utensils.
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