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MedTech Outlook | Monday, March 14, 2022
Sterilization is how living microorganisms are removed from substances. It is used to prolong the life of items and kill germs
FREMONT, CA: Sterilization techniques that are effective in the laboratory are critical when working with isolated cell lines. Naturally, lab personnel or researchers do not want bugs from the environment growing in their excellent culture medium, and cultures must also be sterilized before disposal. Unless they view their cultures through microbiology microscopes, they may be unaware of any unwanted microbe guests. It's time to brush up on laboratory sterilization procedures and how they work to keep their cells healthy, happy, and bug-free.
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In most laboratories, the preferred method of sterilization is autoclaving—heating the material to be sterilized with pressurized steam. This is a highly effective method for killing all microbes, spores, and viruses, though some specific bugs require incredibly high temperatures or long incubation times. Autoclaving effectively kills microbes through the hydrolysis and coagulation of cellular proteins, which is accomplished through high temperatures in the presence of water. As a result, those bugs have no chance. The steam generates intense heat. Pressurized steam has a high latent heat capacity; at 100°C, it retains seven times the heat of the water. This heat is released upon contact with the more excellent surface of the sterilized material, allowing for rapid heat delivery and penetration of dense materials. At these temperatures, water is highly effective at hydrolyzing proteins.
There is one critical distinction between dry heating and autoclaving. There is no water, which means that protein hydrolysis cannot occur. Rather than that, dry heat typically kills microbes by oxidizing cellular components. This requires more energy than protein hydrolysis and thus requires higher temperatures for effective dry heat sterilization. For example, sterilization can typically be accomplished in 15 minutes using an autoclave set to 121°C, whereas dry heating requires a temperature of 160°C to achieve the same result.
Filtration is an excellent method for rapidly sterilizing solutions without heat. Naturally, filters function by passing the solution through a filter with a pore diameter too small for microbes to pass through. Sintered glass funnels made of heat-fused glass particles or, more commonly these days, membrane filters made of cellulose esters are used as filters. Filters with an average pore diameter of 0.2um are typically used to remove bacteria. However, keep in mind that because viruses and phages can pass through these filters, filtration is not an effective method of laboratory sterilization if these are a concern.
While ethanol is frequently used as a disinfectant, isopropanol is a more effective solvent for fat and is probably a better choice. Both solvents work by denaturing proteins, which require water, and thus must be diluted to a concentration of 60–90 percent in water to be effective. Again, while ethanol and IPA effectively kill microbial cells, they do not affect spores.
UV, x-rays, and gamma rays are all types of electromagnetic radiation that cause severe damage to DNA and thus make excellent sterilization tools. Their primary difference in terms of effectiveness is their penetration. Since UV has limited penetration into the air, sterilization occurs in a relatively small area around the lamp. It is, however, relatively safe and quite helpful in sterilizing small spaces, such as laminar flow hoods. X-rays and gamma rays are significantly more penetrating, making them more dangerous but highly effective for large-scale cold sterilization of plastic items, e.g., syringes during manufacturing.
Ethylene oxide can sterilize sensitive equipment such as catheters and stents. By alkylation, ethylene oxide effectively inhibits cell metabolism and replication. Due to the ease with which ethylene oxide is absorbed, equipment must be aerated following sterilization to remove any residue. Ethylene oxide is also highly toxic and may cause various health problems. Because it is typically used in healthcare products, you are unlikely to find it in a laboratory.
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