Explain the chemical agents for microbial control.

1. Halogens
- Include fluorine, bromine, chlorine and iodine
- They are Microbicidal, Microbistatic and sporicidal with long exposure – most common - Chlorine and its compounds
- They compounds hychlorites (OCI) chloramines (NH2CL) and gaseous chlorine (CL2) release hypochlorous acid (HOCL) in water
HOCL oxidizes S-H group of amino acids cystein and denatunes enzymes stopping metabolic reaction.

2. Phenol and its derivatives
- Phenol/carbolic acid is a poisonous compound delivered from distillation of coal tar
- It has chemically related compounds called phenolic creosols, chlorinated phenols and bisphenols
- Kill by disrupting cell walls, cell membrane and precipitating proteins
- They inactivate enzyme systems

3. Alcohol
- Common suitable are ethanol and isopropyl –alcohol. At concentration above 50%. They dissolve membrane lipids; disrupt cell surface tension destroying the cell.
- Solution of 50 to 95% with water denature proteins by coagulation
- Absolute alcohol (100%) dehydrates cells and inhibits their growth.

4. Hydrogen peroxide (H2O2)
- Is a colorless liquid that decomposes in the presence of light metals catalyses into water and oxygen
- The solution is bactericidal, virucidal, fungicidal and in higher concentrations sporicidal
- The oxygen forms hydroxyl free radical (OH) which are toxic and reactive to cells

5. Heavy metal compounds
- Higher molecular weight metals – mercury, silver, copper are very toxic in minutes quantities
- The heavy metal germicides occur inform of aqueous solutions, ointment or soaps
- The metals bind into functional group of proteins and inactive them hence stopping metabolism
- They destroy all microbes except Endospore.

6. Aldelydes
- Commonly used aldehydes are glutaraldehyde and formaldeliyde
- Glutaraldehyde disrupts the activity of enzymes in the cell
- It kills spores, viruses, fungi and vegetative bacteria including mycobacterium and pseudomonas
- Formaldelyde is an irritating gas that readily dissolves in water to form an aqueous solution – formalin
- It kills by attaching to nucleic and functional groups of amino acids

7. Detergents (chemicals with surface action)
Include soap (anionic detergents) and quaternary ammonium compounds – quats – (cationic detergents)
- The positively charge ends of quats bind with negatively charge bacterial surface proteins and disrupt the cell membrane making it loose selectively permeability leading to death of the cell.
- At high concentrations quats are effective against vegetative forms but not spores
- Soaps are alkaline compounds made by combining the fatty acids oils with sodium or potassium salts
- They are weak microbicides and only destroy highly sensitive forms vegetative cell e.g. gonorrhea, meningitis and syphilis bacteria’

8. Acids and alkalis
Very low or high PH destroys or inhibits microbial cell growth
- Aqueous solution of ammonium hydroxide are common compound of detergents and deodorizers
- Organic acids are used in food preservation they prevent spore germination, bacterial and fungi growth e.g. propionic acid is added into bread and cake to retard molds
- Benzoic and sorbic acid are added to beverages, syrups and margarine to inhibit yeast.

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Kavungya answered the question on March 13, 2019 at 06:09