Methods of Sterilization and Disinfection

Disinfection is usually carried out by using disinfectants (chemicals). Some disinfectants may be very effective and have a wide spectrum (have the capability of destroying a wide variety of microorganism) while others may have a narrow spectrum but, they may be easy to use, be non toxic or inexpensive.

Sterilization can be done by three methods: physical, chemical and physiochemical. Physical method includes heat, radiation, and filtration. Chemical methods involve using liquid and gaseous chemicals. Physiochemical is a combination of physical and chemical method.

Types

Disinfection

·         Air disinfectants - disinfectant is dispersed as either as an aerosol or vapor at a sufficient concentration in the air to cause the number of viable infectious microorganisms to be significantly reduced. Chemicals used propylene glycol and triethylene glycol.

·         Alcohols - high-concentration can effectively inactivate viruses such as HIV, hepatitis B, and hepatitis C. Chemicals present usually ethanol or isopropanol. It is safe and inexpensive to use in household environment, care has to be taken around inflammable items.

·   Aldehydes – are somewhat effective on spores and fungus also. Chemicals - formaldehyde and glutaraldehyde.

·       Oxidizing agents – Cause the microorganism to collapse. Chlorine and oxygen are strong oxidizers, so their compounds are used for e.g. common household bleach. In fact it is the most cost-effective home disinfectant (sodium hypochlorite solution) is used to clean toilets, drains, surfaces, swimming pool.

·  Phenolics – It is oldest known disinfectant for e.g. mouthwashes, Dettol. Chemicals - Phenol, Chloroxylenol

·     Quaternary ammonium compounds ("quats") – These are effective low level disinfectants. Chemicals - benzalkonium chloride.

·         Biguanide polymer polyaminopropyl biguanide - bactericidal at very low concentrations (10 mg/l)

·         High-intensity shortwave ultraviolet light are used to disinfect smooth, opaque materials.

·         Common sodium bicarbonate (NaHCO3) has disinfectant properties.

Sterilization

·       Steam - Used in machines called autoclaves. Autoclaves use steam heated to 121–134 °C (250–273 °F). To achieve sterility, a holding time of at least 15 minutes at 121 °C (250 °F) or 3 minutes at 134 °C (273 °F) is required. Autoclave treatment inactivates all fungi, bacteria, viruses and also bacterial spores. Pressure cooking food is also steam sterilization though it is not that thorough.

·    Heating – Under heating flaming, incineration, boiling in water, tindalization, dry heat. These methods inactivate and kill microorganisms in objects like glass, metals. Boiling in water for 15min inactivates viruses and kills most vegetative bacteria. However it has no effect on the spores. Tindilization means boiling for 20 minutes and then cooling, again re-boiling and cooling for three times. This method is more effective on sporulating bacteria than just boiling. Dry heat method can be used on powders and items that bear very high them of heat.

·  Chemical sterilization – Chemicals like Ethylene oxide, Ozone, Bleach, Glutaraldehyde and Formaldehyde, Phthalaldehyde, Hydrogen Peroxide, Dry sterilization process, Peracetic acid and Silver are used in varying degrees. Products that can get damaged due to heat are subjected to chemical sterilization for e.g. biological materials, fiber optics, electronics, and plastics. Ethylene oxide gas and Ozone gas oxidize most organic matter. Though bleach and Glutaraldehyde and formaldehyde solutions is used as a disinfectant, it’s a much more concentrated in sterilization also infected item is left immersed for long duration for effective sterilization. Dry sterilization process with chemicals is useful for sterilizing plastic bottles medical and pharmaceutical applications.

·    Radiation sterilization - Electron beams, X-rays, gamma rays, or subatomic particles are used for sterilizing disposable medical equipment, such as syringes, needles, canulas, IV sets and biological safety cabinets between uses.

·       Sterile filtration - Clear liquids that would be damaged by heat, irradiation or chemical sterilization can be sterilized by mechanical filtration. Filtration is done through pores that are smaller in size than the organism in question and this has to be done very slowly.