Question

For each of the 7 groups of chemical agents, identify the mechanism of action and determine if the agent is capable of sterilizing or only disinfecting.

Answer 1

7 groups of chemical agents

1. Alcohol
2. Phenol and phenolic compounds
3. Halogen compounds
4. Heavy metals and their compounds
5. Aldehydes
6. Gaseous agents
7. Detergents

1. Alcohol :

Alcohol causes death of microorganisms by denaturing the cellular proteins. Ethanol is the most commonly used alcohol for controlling microorganisms.

Mechanism of action : Alcohol is a lipid solvent that damages the lipid bilayer of cell membrane and cell wall. It solubilizes the lipid bilayer of cell wall and membrane and creates pores. The remaining alcohol enters into the cytoplasm through the pore and denature the cellular proteins killing the bacteria.

Alcohol is used as disinfectant. They can be used as sanitizer on skin and disinfectant to clinical instruments.

2. Phenol and phenolic compounds

Phenol are active against a wide range of micro-organisms including some fungi and viruses, but has less effective against spores. Vegetative cells of microorganisms are killed rapidily.

Mechanism of Action : Phenol and phenolic compounds kills the microorganisms by varities of effects such as disruption of cell, precipitation of cellular protein, inactivation of enzymes and leakage of cellular materials.

Phenols can be used as disinfectant and antiseptic. Lysol used as disinfectant while dettol and savlon used as antiseptic.

3. Halogen compounds

Halogen compounds are chemicals used for water and sanitation. Iodine and Chlorine are two major elements used in halogenic compounds. Halogen compounds mechanism differ when different halogens used.

(i) Iodine

Mechanism of action : Iodine is powerful oxidizing agents and irreversibly oxidises the cellular materials.Iodine also brings halogenation of tyrosine residue of protein and enzymes and inactivates it.

(ii) Chlorine

Mechanism of action : Chlorine is in the form of hypochlorite or chloramine. When it is added in water, free chlorine is releases which form hypochlorous acid (HClO). Hypochlorous acid decomposes to release nascent oxygen which is powerful oxidizing agent and kills the microorganisms by oxidizing the cellular components. Chlorine and chlorine compounds also inactivates the proteins and enzymes by direct chlorination.

Halogen compounds mainly used as disinfectant. Sometimes used in antiseptic ointments.

4. Heavy metals and their compounds

They are capable of antimicrobial action. Most effective and commonly used are Mercucry (Hg), Silver (Ag) and Cupper (Cu).

Mechanism of action : Heavy metals and their compounds combines directly with cellular proteins and enzymes and inactivates them. High concentration of heavy metals salts also coagulates and precipitates the cellular proteins and kills the microorganisms.

Heavy metal and their compounds are used as disinfectant.

5. Aldehydes :

Formaldehyde and Gluteraldehyde are commonly used aldehydes for antimicrobial purpose.

Mechanism of action : Acts through alkylation of amino, carboxyl, or hydroxyl group, and probably damages nucleic acids. It kills all microorganisms, including spores.

Aldehydes are usually used as sterilizer for sterilizing devices such as catheters, Operation theaters, and respiratory therapy instruments.

6. Gaseous agents :

Ethylene oxide and β-propiolactone are commonly used gaseous sterilizing agents.

Mechanism of action : Alkylation reactions with organic compounds inactivates enzymes having sulfhydryl group and other proteins.

Gaseous agents are used for sterilizing. It has high penetrating power and passes through large packages of materials, bundles of cloth, and even certain plastics and sterilizes them.

7. Detergents :

Detergents are used primarily for cleaning purposes but it has also antimicrobial properties.

Mechanism of action : Detergents kills the microorganisms by denaturing proteins and enzymes and interfering with glycolysis. Detergents also damages cell wall and cell membrane.

Detergents are used as disinfectants, sanitizers and antiseptic. They are used to disinfect hospital floor.