Working under pressure is no fun. Deadlines, stress, headaches, a demanding boss. But if you’re an autoclave, you work best under pressure. In fact, you only work under high-pressure conditions. In this post we will explore how autoclaves work under the high-pressured conditions of steam and heat to kill microorganisms. We will also look at how the autoclave’s function is similar to a pressure cooker, and what
the basic phases of an autoclave cycle are. Haga click aquí para leer este texto en español As we explained in our first post on microbiology, microorganisms need food, the right temperature, and enough moisture to survive and
reproduce. So why not just starve them or dry them out? Since microorganisms can survive on tiny amounts of nutrients and moisture, these methods are not effective enough. Moreover, the spore, a kind of bacteria that lives in a quasi-hibernation state, can survive in extremely inhospitable conditions. So if neither of these methods work, how can we destroy microorganisms? The answer is heat. Heat destroys the
proteins inside of the microorganisms, a process called denaturalization. In order to understand how this works, let’s take a look at the two ways we can cook an egg.
(L) The poached egg causes the egg to become white and hard, thus coagulating. (R) Here two eggs are burnt in the frying pan, an example of oxidation Steam sterilization, in the form of an autoclave, uses the first method, coagulation, to kill microorganisms. That means that the autoclave chamber acts similarly to that pot of boiling water that poached the egg. The key ingredient that they both share is the presence of steam, or the gaseous state of water. The steam inside the autoclave is the agent by which the moist heat attacks the microorganisms, thus causing them to coagulate and die. In order to understand how autoclaves use the power of steam to kill microorganisms, we will explore how a pressure cooker functions. A Souped-up Pressure CookerThe word “autoclave” comes from the Latin “auto” (self) and “clavis” (key), in other words, a self-locking device. The autoclave’s basic functionality is quite similar to that of a pressure cooker, a type of saucepan that is able to cook food 50-70% faster than regular cooking methods. View of the inside of a pressure cooker Take some raw food, for example beans, and place it inside the pressure cooker with water or other liquid, and then seal the vessel with the special locking lid, which includes a round rubber gasket used to seal in the steam. Place on the fire at high heat and wait for the temperature to rise and the steam to start escaping. Inside the sealed chamber the steam will expand and push out the remaining air through the air exhaust valve. Lower the flame and let the pressure cooker continue to cook without touching the valve or the lid. Notice that the air exhaust valve allows some of the steam to escape, so that the pressure doesn’t build up too much, thus preventing an explosion. This “efficient kitchen delight” literally forces the heat inside of the food by using:
Here Comes the AutoclaveLike the pressure cooker, an autoclave is a machine that uses the combination of high pressure and steam in order to transfer heat to the items placed inside. Invented in 1879 by Charles Chamberland, the first autoclave was essentially a glorified pressure cooker. And just as the pressure cooker has gone through countless design upgrades in the last few centuries, so has the autoclave. From basic, mechanical machines to fully computerized, sophisticated masterpieces of sterilization, autoclaves have come a long way. Today, hospitals, laboratories and doctors’ offices use autoclaves to sterilize solid and hollow equipment, supplies, fluids, and waste. And in the chemical industries, autoclaves vulcanize rubber, cure coatings, and synthesize crystals -- such as in the growing of synthetic quartz and gems. Though autoclaves come in a variety of sizes and models, the basic principle remains: harnessing the power of pressure and steam to kill microorganisms. (L) Before sterilization, the bacteria look healthy and strong. (R) After sterilization, the membranes are cracked and torn from exposure to high temperature steam, thus causing the bacteria to die The Autoclave, a Basic OverviewAs we discussed above, the pressure cooker forces the moist heat inside of the food in order to cook it. Imagine that instead of food you had a tray of surgical supplies ready to be sterilized for tomorrow’s surgery. Placing them inside the autoclave and running a cycle would force the moist heat into all the possible nooks and crannies on the surfaces of the equipment. Here’s the basic overview of an autoclave cycle, which varies, of course, depending on what and how many materials are being autoclaved:
Don't Run out of Steam... We're Just Getting Started!Let’s review: we learned that heat, and specifically, moist heat, is the best way to kill germs. There are two ways to kill using heat, by coagulation or by oxidation. Autoclave sterilization uses coagulation in the form of highly-pressurized steam to denature the proteins inside of the microorganisms. We then compared how a pressure cooker functions to how an autoclave operates. Just as the pressure cooker uses the intense power of steam to force the heat into food, the autoclave also uses steam to “force” steam into the equipment, killing all forms of microbiologic life living on said equipment. And finally we looked at the basic phases of an autoclave cycle, from heating up the water and building pressure, to holding time and cooling down. We hope you’ve enjoyed this introduction into the world of autoclaves. Just be thankful you are not a little bacteria experiencing it firsthand. Check out our next post, “Sterilization by Steam,” in which we will explore the science of using steam as a sterilizing agent in the autoclave. Comments and questions are welcome, as always, in the comment section below. (Post based on Sterilization of Medical Supplies by Steam by Jan Huys. Images of bacteria before and after sterilization appear with permission from Huys.) Haga click aquí para leer este texto en español Tuttnauer Team is made up of veteran staff at Tuttnauer that are responsible for communicating with our customers about sterilization and infection control. Let us know if there is anything specific you want to read more about. What are the 4 cycles of an autoclave?There are, in general, four standard sterilization cycles: gravity, pre-vacuum, liquids, and flash (also known as immediate use).
What is sterilization using steam heat under pressure called?4.2. 1 Steam Sterilization. Steam sterilization (also called autoclaving) is conducted in an autoclave which is a container that can withstand high pressure and temperature.
What are the 3 stages of autoclave sterilisation?Steam sterilization cycles can be divided into three distinct phases; conditioning, exposure and drying.
In which phase of steam sterilization is the air removed from the chamber?» Heating (come-up) phase - steam enters the sterilizer jacket and air is removed from the sterilizer chamber, either by gravity displacement or mechanically (prevacuum).
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