Different Sterilisation Methods Used in the Lab
Sterilisation can be achieved by a combination of heat, chemicals, irradiation, high pressure and filtration like steam under pressure, dry heat, ultraviolet radiation, gas vapour sterilants, chlorine dioxide gas etc. Effective sterilisation techniques are essential for working in a lab and negligence of this could lead to severe consequences, it could even cost a life if not attended Autoclaves Equipment to.
So what are the most commonly used methods of Sterilization in the laboratory, and how do they work? Read on…
Heat Method
This is the most common method of sterilisation. The heat is used to kill the microbes in the substance. The extent of sterilisation is affected by the temperature of the heat and duration of heating. On the basis of the type of heat used, heat methods are categorised into:
(i) Wet Heat/Steam Sterilisation: In most labs, this is a widely used method which is done 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 by hydrolysis and coagulation of cellular proteins, which is efficiently achieved by intense heat in the presence of water. The intense heat comes from the steam. Pressurised steam has a high latent heat and at 100oC it holds 7 times more heat than water at the same temperature. In general, Autoclaves can be compared with a typical pressure cooker used for cooking except in the trait that almost all the air is removed from the autoclave before the heating process starts. Wet heat sterilisation techniques also include boiling and pasteurisation.
(ii) Dry heat sterilisation: In this method, specimens containing bacteria are exposed to high temperatures either by flaming, incineration or a hot air oven. Flaming is used for metallic devices like needles, scalpels, scissors, etc. Incineration is used especially for inoculating loops used in microbe cultures. The metallic end of the loop is heated to red hot on the flame. The hot air oven is suitable for dry material like powders, some metal devices, glassware, etc.
Filtration is the quickest way to sterilise solutions without heating. This method involves filtering with a pore size that is too small for microbes to pass through. Generally filters with a pore diameter of 0.2 um are used for the removal of bacteria. Membrane filters are more commonly used filters over scintered or seitz or candle filters. It may be noted that viruses and phage are much smaller than bacteria, so the filtration method is not applicable if these are the prime concern.
Radiation sterilisation
This method involves exposing the packed materials to radiation (UV, X-rays, gamma rays) for sterilisation. The main difference between different radiation types is their penetration and hence their effectiveness. UV rays have low penetration and thus are less effective, but it is relatively safe and can be used for small area sterilisation Scientific Supplies Australia. X-rays and gamma rays have far more penetrating power and thus are more effective for sterilisation on a large scale. It is, however, more dangerous and thus needs special attention. UV irradiation is routinely used to sterilize the interiors of biological safety cabinets between uses. X-rays are used for sterilising large packages and pallet loads of medical devices. Gamma radiation is commonly used for sterilisation of disposable medical equipment, such as syringes, needles, cannulas and IV sets, and food.
Chemical method of sterilisation: Heating provides a reliable way to get rid of all microbes, but it is not always appropriate as it can damage the material to be sterilised. In that case, chemical methods for sterilisation is used which involves the use of harmful liquids and toxic gases without affecting the material. Sterilisation is effective using gases because they penetrate quickly into the material like steam. There are a few risks, and the chances of explosion and cost factors are to be considered.
The commonly used gases for sterilisation are a combination of ethylene oxide and carbon dioxide. Here Carbon dioxide is added to minimize the chances of an explosion. Ozone gas is another option which oxidize most organic matter. Hydrogen peroxide, Nitrogen dioxide, Glutaraldehyde and formaldehyde solutions, Phthalaldehyde, and Peracetic acid are other examples of chemicals used for sterilisation. Ethanol and IPA are good at killing microbial cells, but they have no effect on spores.