Use of Chemical agents in microbial control:

The chemical agents are mostly employed in disinfection and antisepsis. The proper use of these agents is essential to laboratory and hospital safety. Factors such as the kinds of microorganisms potentially present the concentration and nature of the disinfectant to be used and the length of treatment should be considered. 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, at high dilutions and in the presence of organic matter and should not be toxic to people or corrosive for common materials. The disinfectant must be stable upon storage, odorless or with a pleasant odor, soluble in water and lipids for penetration into microorganisms, and have a low surface tension so that it can enter cracks in surfaces.

Phenols:

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. Phenolics are tuberculocidal and effective in the presence of organic material and remain active on surfaces long after application. However, they do have a disagreeable odour and can cause skin irritation. Hexachlorophene has been one of the most popular antiseptics because once applied it persists on the skin and reduces skin bacteria for long periods.

Alcohols:

Alcohols are the most widely used disinfectants and antiseptics. They are bactericidal and fungicidal but not sporicidal. Ethanol and isopropanol are the two most popular alcohol germicides. They act by denaturing proteins and possibly by dissolving membrane lipids. Small instruments like thermometers can be disinfected by soaking them for 10 to 15 min in alcohol solutions. A 70% ethanol is more effective than 95% as water is needed for proteins to coagulate.