Sterilization is the technique via which all viable cells, spores and acellular entities for example viruses, viroids, virusoids and prions are either removed or destroyed from a habitat or object. An object can be termed as sterile when it is totally free of viable microbes and other infectious agents. On the other hand, disinfection is the process of killing, removing or inhibiting microorganisms that may result in causing a disease. Sanitization is another term which is quite closely correlated to disinfection. During sanitization, the population of micro-organisms is lowered to levels that can be considered safe by the standards of public health. The inhibition of microbial growth and destruction of microorganisms and are not simple as the efficiency of an antimicrobial agent is affected by at least the following six factors:
🗸 Population Size
🗸 Population Composition
🗸 Concentration or Intensity of an Antimicrobial Agent
🗸 Contact Time
🗸 Temperature
🗸 Local Environment
The control of microorganisms in a laboratory or a medical facility can be brought about by two broadly divided methods namely Physical and Chemical Methods:
Physical Control Methods
• Heat: Moist heat is able to readily destroy viruses, bacteria and fungi. Moist heat kills by degrading nucleic acids and denaturing enzymes and other essential proteins. Exposure to boiling water for 10 minutes is enough to destroy vegetative cells and eukaryotic spores. But boiling is not sufficient to destroy bacterial spores as boiling does not sterilize. For the destruction of bacterial endospores, moist heat sterilization must be carried out at temperatures above 100°C and this requires the use of saturated steam under pressure. Steam sterilization is carried out with an autoclave usually at 121°C and 15 pounds of pressure for at least 15 minutes for a margin of safety. No doubt larger containers of liquid such as flasks and carboys require much longer treatment times. Many objects are best sterilized in dry heat, appropriate for moisture-sensitive substances.
• Filtration: The method of filtration among sterilization techniques is one of the unique methods as rather than destroying, it removes microorganisms. Since it has the capability of prevention of both viable and nonviable particles, therefore it can be utilized for the sterilization and clarification of both gases and liquids. Sieving, adsorption, and to trap within the matrix of the filter material are the primary methods involved in the process of filtration. Filtration utilizes membranous channels that have little pores that let the fluid pass through yet forestall greater particles like microscopic organisms from going through the channel. Thus, the smaller the pore, the more probable the channel is to prevent more things from going through it. HEPA filters, glass fiber filters, glass wool depth filters and hydrophobic membrane filters are some of the examples.
• Radiation: Microbial DNA remains the major target for radiations. The damage is brought about by the free radical production and ionization. Ranging from 150-3900 Å, Ultraviolet radiation has the highest bactericidal effect at 2600 Å. Exposure to such waves result in the formation of pyrimidine dimers that incorporate error in DNA replication causing the death of microorganisms due to mutation. It is therefore, applied for disinfecting air, sterilizing the surface of aseptic work territories, and treating manufacturing-grade water.
Chemical Control Methods
• Ethylene Oxide: Ethylene oxide (EO) gas is a typical gas utilized for chemical treatment applied to disinfect and sterilize various kinds of hardware and surfaces as a result of its wide scope of compatibility with various materials. The mode of action of this antimicrobial gas is by the alkylation of sulphydryl, hydroxyl, amino and carboxyl groups and imino groups and proteins of nucleic acids. This technique, however, isn't without disadvantages as the degree of gas in the sterilizer continues diminishing because of absorption, and the treated materials need to go through a cycle of desorption to eliminate the poisonous residual wastes.
• Formaldehyde: Formaldehyde is obtained by heating formalin (37%w/v) at around a temperature of 70-80°C. It is another important gas used for sterilization which is highly reactive. Possessing broad-spectrum biocidal activities, it has found its application in specific, diagnostic, medical and electrical equipment and the sterilization of reusable surgical instruments.
• Hydrogen peroxide: A liquid chemical sterilizing agent, hydrogen peroxide is a strong oxidant which can destroy a wide range of microbes. It finds its use for sterilizing temperature or heat-sensitive equipment such as endoscopes. A high concentration of (35-90%) is used in medical applications.
• Glutaraldehyde: Glutaraldehyde is an acknowledged liquid sterilizing agent that requires comparatively longer time of immersion. It needs as long as 22 hours of immersion time for removal of all the spores. Glutaraldehyde’s use is therefore restricted to certain surfaces that have lesser contamination.
• Hypochlorite: Also known as liquid bleach, hypochlorite solution acts by oxidizing organic compounds resulting in modification of microbial protein. Appropriate hypochlorite concentrations can be utilized to disinfect workstations and also surfaces for cleaning blood spills and other liquids.