Is there anything more annoying than finding your culture medium contaminated? Thankfully, there are a number of effective sterilization techniques that you can use in the lab to avoid finding yourself in this situation. Some of the most commonly used laboratory sterilization techniques include heat sterilization, chemical sterilization and radiation sterilization but for the purpose of this article, we will be limiting our discussion to heat sterilization, specifically naked flame sterilization or “flaming” and radiation sterilization involving infrared sterilizers.
Some of the most common forms of heat sterilization techniques include autoclaving (moist heat sterilization), dry heat sterilization, glass bead sterilization, tyndallization and flaming. During the process of flaming, the material is directly subjected to the flame of an alcohol lamp or Bunsen burner to deactivate, kill, destroy and eliminate any infectious agents (e.g. microbes, viruses, prion proteins) that may be present in your instruments and surfaces. Basically, this technique is ideally used for small metal or glass objects (e.g. inoculating loops and straight wires) and is not applicable for larger objects.
While subjecting objects to extremely high temperatures over a specified period of time can eliminate various pathogenic agents, is convenient and relatively inexpensive, and will not cause metals to corrode or release harmful fumes during the process, there are also a lot of disadvantages in using this technique.
- Flaming is a relatively slow process and can take a couple of hours to complete.
- Not all objects can withstand the temperature required for flaming. Plastics will melt when subjected to this method.
- It increases the risk of contamination. When an object is subjected to open flames, not all infectious materials will be deactivated and killed instantly. Some may be sprayed on nearby surfaces and objects, so you’ll need a heated cage to contain the sprayed microorganisms and reduce the likelihood of further contaminating your work area.
- It may leave carbon residues on the heated object. If not heated enough, flaming may leave carbon and other chemical residues on the heated object. To reduce this risk, you may dip the object in 70% ethanol before subjecting it to an open flame.
- Flaming can be highly dangerous. Bunsen burners use highly flammable gas or alcohol and are often left burning. This presents a fire hazard in the lab.
Considering the many disadvantages and the inherent risks of flaming, you may want to consider other methods of sterilization such as using infrared (IR) sterilizers in the laboratory. After all, infrared sterilizers are proven to be just as effective as flaming in getting the job done.
IR sterilizers use non-ionizing radiation to destroy microorganisms. However, since non-ionizing radiation has longer wavelength and lower energy compared to ionizing radiation, it cannot penetrate substances and can only be used in sterilizing surfaces.
Using an IR sterilizer may work to your advantage since it involves a shorter cycle time (complete sterilization can be achieved in 5 to 7 seconds) and consumes less energy (can generate 900o to 1300o within a fraction of a second, does not need time to warm up and does not produce excess heat). Additionally, IR sterilizers do not leave any chemical residues and do not produce any adverse toxicologic or environmental effects. And since it does not have any moving parts, wear and tear is kept at a minimum.
IR sterilizers are completely safe and convenient to use and can be ideally used for culture tube and pipette mouths, platinum inoculating hoops, needles, tweezers and other small instruments. It can also be used for sterilizing various metal and borosilicate glass instruments. Perhaps the only drawback in using infrared sterilizers is its prohibitive price, which can go up to $1000.