Ultraviolet (UV) radiation is a low-energy electromagnetic radiation that can kill various microorganisms. Gram-negative bacteria are the most sensitive, followed by Gram-positive bacteria, and spores are the least sensitive. The resistance of fungal spores is the strongest. The direct effect of UV radiation is to inactivate microorganisms by destroying their nucleic acids and proteins, while the indirect effect is to kill microorganisms through the ozone produced by UV irradiation. Direct irradiation of the culture room for disinfection is simple and effective.
The disinfection effect of a UV lamp is positively correlated with its radiation intensity and irradiation dose. The radiation intensity decreases as the distance between the lamp and the object increases, and the irradiation dose is proportional to the irradiation time. Therefore, the distance and irradiation time of the UV lamp should be appropriate for the object to be irradiated. A 30W lamp 2 meters above the ground can irradiate a 9 square meter room. It is recommended to irradiate for 2 to 3 hours per day with a 30-minute interval. The irradiation time should be extended if the lamp is located more than 2 meters above the ground, and the irradiation effect is poor at a distance of 2.5 meters. The distance between the UV lamp and the working table should not exceed 1.5 meters, and the irradiation time should be 30 minutes. The UV lamp not only harms the skin and eyes but also has adverse effects on cultured cells and reagents, so the UV lamp should not be operated while handling cell culture wares.
The most common method of high-temperature humid sterilization is the autoclaving method, which has good penetration ability for biological materials and can cause microbial death by protein denaturation and coagulation. This method can be used to sterilize fabrics, glassware, metalware, rubber products, and certain culture media.
Different autoclaves reach different temperatures, and the effective sterilization pressure and time required for different disinfection items are different. After taking out the sterilized cell culture ware (excluding liquids) from the autoclave, they should be immediately dried in an oven at 60 to 70 ℃ and stored for later use, otherwise, the moist packaging material may be contaminated by microorganisms. Boiling sterilization is also a commonly used method of moist heat disinfection, which is characterized by simple conditions and convenient use.
Dry heat sterilization involves heating items in an electric oven to above 160 ℃ and keeping them there for 90 to 120 minutes to kill bacteria and spores and achieve sterilization. This method is mainly used to sterilize glass cell culture products (such as large beakers and culture bottles), metalware, and items that cannot come into contact with steam (such as powder and oil preparations).
After dry heat sterilization, turn off the switch and let the items gradually cool down before opening the oven. Do not open the oven immediately to avoid sudden temperature changes that may cause the glassware to rupture. There should be space between items in the oven, and the items should not be close to the heating device. Burn injury is also one of the sterilization methods, which often involves using the flame of an alcohol lamp on the table to scorch the mouth of metalware and glassware for sterilization purposes.
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