Disinfection is the process of destruction of pathogenic or potentially pathogenic microorganisms by chemical means. All specimens, cultures and other material that have been examined in a laboratory must be made non-infectious before being discarded or leaving the laboratory.
This is necessary to protect all those health professionals working in the laboratory and the members of the general public who may handle the waste materials before its final disposal.
Ideally all material should be sterilized. Unfortunately it is not always possible to achieve this. But the most recommended method is the destruction of the vegetative forms of all pathogenic organisms. Laboratory waste, which includes articles that will be reused, may be disinfected by chemical or physical means.
Decontamination using chemical disinfectants
Decontamination is the process of decreasing the virulence (ability to cause disease) of microorganisms by using different chemical agents.
A. Phenolic compounds
Phenolic compounds are a broad group of agents, were among the earliest germicides. However, more recent safety concerns restrict them their use. They are active against vegetative bacteria and lipid containing viruses, and when properly formulated, also show activity against mycobacteria.
They are not active against spores and their activity against non-lipid viruses is variable.
Many phenolic products are used for the decontamination of environmental surfaces, and some (example, triclosan and chloroxylene) are among the more commonly used antiseptics. They are used at 2 – 5% volume/volume (v/v) concentration according to the manufacturer’s instruction. Dilutions should be kept for more than twenty-four hours.
B. Chlorine (sodium hypo chloride)
Chlorine, a fast – acting oxidant, is a widely available and broad-spectrum chemical germicide. It is normally sold as bleach, an aqueous solution of sodium hypo chloride, which can be diluted with water to provide various concentrations of available chlorine. Products containing 100,000 parts per million (ppm) of chlorine are suitable for laboratory use. They are effective against viruses as well as bacteria. Dilutions should not be kept for more than 24 hours so as to maintain its activity.
Ethanol and isopropanol, at 70 -80% volume / volume (v/v) concentration in water, are useful for skin, work surfaces of laboratory benches and biosafety cabinets, and to soak small surgical instruments. They are active against vegetative bacteria, fungi and lipid containing viruses, but not against spores. Their activity is improved by mixing them with formalin or hypochlorite. A major advantage of aqueous solutions of alcohols is that they do not leave any residue on treated items.
Formaldehyde is a gas that kills all microorganisms and spores at temperatures above 200C. It is relatively slow acting chemical and needs a relative humidity level of about 70%. Five percent (5%) formaldehyde is widely used for decontamination and disinfection of enclosed volumes such as safety cabinets and laboratory rooms.
Like formaldehyde, glutaraldehyde is also active against vegetative bacteria, spores fungi and lipid and non- lipid containing viruses. It is non-corrosive and faster acting than formaldehyde. However, it takes several hours to kill bacterial spores.
F. Iodine and iodophors
Iodine and iodophors have similar action to that of chlorine. Iodophors and tincture of iodine are good antiseptics. Iodine can be toxic. Organic iodine based products must be stored at 4 -100°C to avoid the growth of potentially harmful bacteria in them.Caution: Most of the disinfectants are toxic and irritant to skin and mucous membranes. Therefore, dilutions should be made in fume – hood or in well ventilated areas.
Decontamination of laboratory space
Decontamination of laboratory space, its furniture and equipment requires a combination of liquid and gaseous disinfectants. Laboratory surfaces can be decontaminated using a solution of sodium hypochlorite. A solution containing 1g/ l available chlorine may be suitable for general environmental sanitation. However, stronger solutions of chlorine (5g/l) are recommended when dealing with high-risk situations. For environmental decontamination, formulated solutions containing 3% hydrogen per oxide make suitable substitutes for bleach solutions.