Microbiology

Chemical Agents Used Against Microorganism

As we know there are many chemicals available to kill microorganisms. But correct choice of chemical is necessary at the place and environment of object and it’s surrounding. Here we will discuss major groups of chemicals those are used in different conditions to kill or prevent microorganisms.

Major Group Of Chemical Antimicrobial Agents

The major antimicrobial agents can be grouped as follow:

  1. Phenol and phenolic compounds
  2. Alcohols
  3. Halogens
  4. Heavy metals and their compounds
  5. Dyes
  6. Detergent
  7. Quaternary ammonium compounds
  8. Aldehydes
  9. Gaseous agents

Phenol And Phenolic Compounds

Phenol has the distinction of being used successfully in the 1880s by Joseph Lister, a surgeon, to reduce infection of surgical wounds. As Lister become aware of pasteur’s studies which incriminated germs as the cause of infection. Accordingly, he instituted the practice of applying a solution of phenol (carbolic acid) to surgical incisions and wounds, the reduction in infection was striking. Later he developed the practice of applying phenol into the operating room area to control infection.

Because of its best quality of destruction of microorganisms, phenol become the standard against which other disinfectants of similar chemical structure are compared to determine their antimicrobial activity. The procedure used is called the phenol coefficient technique.

Phenol and phenolic compounds are very effective disinfectants. A 5% aqueous solution of phenol rapidly kills the vegetative cells of microorganisms; spores are much more resistant.

Practical Applications

Phenolic substance may be either bactericidal or bacteriostatic, depending upon the concentration used. Bacterial spores and viruses are more resistant than vegetative cells. Some phenolic are highly fungicidal. The antimicrobial activity of phenolic is reduced at an alkaline pH and by organic material. Low temperature and the presence of soap also reduce the antimicrobial activity.

Mode Of Action

Depending upon the concentration of phenolic compounds to which microbial cell is exposed, produce a variety of effects. These include distraction of cell, precipitation of cell protein, inactivation of enzyme, and leakage of amino acids from the cell. Although a specific mode of action is not clear. There is a consensus that the lethal effect is associated with physical damage to the membrane structures in the cell surface, which initiates further deterioration.

Alcohols

Ethyl alcohol, in concentration between 50 to 90% are effective against vegetative cells or nonspore forming cells. For practical application a 70% concentration of ethyl alcohol is used.

Ethyl alcohol cannot be relied upon to produce a sterile condition. Concentration which is effective against the vegetative cells are practically inert against bacterial spores.

There is one record of survival of anthrax spores in alcohol for 20 years and another one of Bacillus subtilis for 9 years.

Methyl alcohol is less bactericidal than ethyl alcohol. Furthermore it is highly poisonous. Even the fumes of this compound may produce permanent injury to the eyes, and is not generally employed for the destruction of microorganisms.

As the molecular weight increases of alcohol, it become more bactericidal. But alcohols of higher than propyl alcohol are not miscible in all proportions with water, they are not commonly used as disinfectant.

Propyl and isopropyl alcohols in concentrations ranging from 40 to 80 % are bactericidal for vegetative cells.

Mode Of Action

Alcohols are protein denaturants, and this property may, to a large extent, account for their antimicrobial activity.

Alcohols are also solvent for lipids and there for may also rupture cell membrane and kill microorganisms. They are also dehydrating agents.

Halogens

Iodine is one of the oldest and most effective germicidal agents. It is in use since 1830. Pure iodine is a bluish-black crystalline element having a metallic luster.  It is only slightly soluble in water but readily soluble in alcohol and aqueous solution potassium or sodium iodide.

Practical Applications

Iodine is a highly effective bactericidal agent and is unique in that it is effective against all kind of bacteria. Iodine also possesses sporicidal activity. However, the rate at which the spores are killed is markedly influenced by the condition  under which they are exposed.

Iodine solutions chiefly used for the disinfectant of skin, and for this purpose they rank among the best disinfectant.

Mode Of Action

The mechanism by which iodine exerts it’s antimicrobial activity is not specifically understood. Iodine is an oxidizing agents, and this fact may account for its antimicrobial action.

Reference: Microbiology by Pelczar

Gaurav Singh

Editor in Chief Medical Microbiology & Recombinant DNA Technology (RDT) Labs - RDT Labs Magazine

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