The chemical agents are mostly employed in disinfection and antisepsis. The proper use of these agents is essential to laboratory and hospital safety. Many disinfectants are available and each has its own advantages and disadvantages, but ideally the disinfectant must be effective against a wide variety of infectious agents. The disinfectant must be stable upon storage, odorless, or with pleasant order, soluble in water and lipids for penetration into microorganisms, and have a low surface tension through that it can enter cracks in surfaces.
In 1867, Joseph Lister employed it to reduce the risk of infection during operations and phenol was the first widely used antiseptic and disinfectant. Today phenol and phenolics such as cresols, xylenols, and orthophenylphenol are used as disinfectants in laboratories and hospitals. Lysol is made of a mixture of phenolics which is commercially available disinfectant. They act by denaturing proteins and disrupting cell membranes.
Alcohols are the most widely used disinfectant and antiseptic. They are bactericidal and fungicidal but not sporicidal. Ethanol and isopropanol are the two most popular alcohol germicides. Small instruments like thermometers can be disinfected by soaking them for 10 to 15 minutes in alcohol solutions. 70% ethanol is more effective than 95% as water is needed for proteins to coagulate.
Halogens exist as diatomic molecules in the free state and form salt like compounds with sodium and most other metals. Iodine and chlorine are the most important antimicrobial agents. Spores can be destroyed at higher concentration. Iodine is often applied as tincture of iodine, 2% or more iodine in a water-ethanol solution of potassium iodide. Skin scars result and sometimes iodine allergies can result.
Chlorine is mostly used as a disinfectant for municipal water supplies and swimming pools and also employed in dairy and food industry. It may be applied as chlorine gas, sodium hypochlorite or calcium hypochlorite, all of which yield hypochlorous acid and then atomic oxygen.
- Heavy metals
Heavy metals such as mercury, silver, arsenic, zinc and copper were used as germicides and these have nit been most recently superseded by other less toxic and more effective germicides. A 1% solution of silver nitrate if often added to the eyes of infants to prevent ophthalmic gonorrhea but now erythromycin is used instead of silver nitrate because it is more effective. Silver sulfadiazine is used on burns. Copper sulphate is an effective algicide in lakes and swimming pools. The action of these heavy metals is mostly on the proteins, and they combine often with their sulfhydryl groups, and inactivate them. They may also precipitate cell proteins.
- Quaternary ammonium compounds
Detergents are organic molecules that serve as wetting agents and emulsifiers and are amphipathic in nature and hence solubilize otherwise insoluble residues and are very effective cleansing agents and are efficient from soaps, which are derived from fats.
Only cationic detergent are effective disinfectants characterized by positively charged quaternary nitrogen and a long hydrophobic aliphatic chain. They are mostly used as disinfectants for food utensils and small instruments and as skin antiseptics.
- Sterilizing gases
Gases may also be used as sterilizing agents in order to sterilize many heat-sensitive items such as disposable petri dishes and many syringes, heat-lung machine components, sutures, etc. Ethylene oxide gas is used for this purpose as it readily penetrates packing materials, even plastic wraps and is both microbicidal and sporicidal and kills by combining with cell proteins.
- Hydrogen peroxide
Hydrogen peroxide effects our direct and indirect actions of oxygen as it forms hydroxyl free radical which is highly toxic and reactive to cells. As an antiseptic, 3% hydrogen peroxide serves a variety of needs including skin and wound cleansing, bedsore care and mouth washing. When it is applied to a wound, the enzyme catalase in the tissue decomposes the hydrogen peroxide into water and free oxygen. The oxygen causes the wound tissues to bubble and the bubbling removes microorganism mechanically.
- Acids and alkalis
Aqueous solutions of ammonium hydroxide remain a common component of detergent, cleanser and deodorizers. Organic acids are widely used in food preservatives because they prevent spore germination and bacterial and fungal growth. Acetic acid in the form of vinegar is a picking agents that inhibits bacterial growth, propionic acid is commonly incorporated into breads and cakes to retard molds, benzoic acid and sorbic acids are added to beverages, syrups to inhibit yeasts.