• Disinfection is a process to remove the infection by reducing the number of microorganism present on any site or article.

• Disinfection not necessarily eliminates all microorganisms, but it can reduce the number of microorganism to such a limit, that they can not cause any infection.

• It is not complete or 100% removal of microbial cells.

• It has very less effect on spores.

Disinfectant	Antiseptic
These are the chemicals which are used for the purpose of disinfection.	Antiseptic is the disinfectants, which are applied on skin or any living tissue, and this process is called antisepsis.

Difference between Disinfection and Sterilization

Sterilization	Disinfection
Complete removal of all forms of cells i.e. vegetative cells, spores, virus particles.	Not complete removal; only reduction in the number of vegetative cells, less effective against viruses.
Mainly physical methods are involved.	Mainly chemical methods are used.
Effectively destroys spores.	Very less effective against spores.
Used for culture media, pharmaceutical drugs, parenteral products, surgical items etc.	Mainly used for surface sterilization, over skin and for hospital sanitization purposes.

Classification of Disinfectants

Based on Consistency:

• Liquids: Alcohol, Phenol, Aldehydes, Halogens, Quaternary ammonium compounds, Biguanides, Acids and esters
• Gases: Formaldehyde vapors, Ethylene di-oxide, Propylene oxide, β-Propiolactone

Based on Spectrum of Activity:

• High Level:These chemical agents kills vegetative microorganism, fungi and also inactivate virus, but not effective against spores.
  Examples: Hydrogen peroxide, Aldehydes, Glutaraldehydes
• Intermediate Level: These chemicals kills vegetative cells, all fungi and most viruses, no affect on spores.
  Examples: Alcohols, Chlorine, Hypochlorites, Phenols
• Low Level:These chemicals kills vegetative microbial cells, some fungi and very few viruses, no effect on spores.
  Examples: Quaternary ammonium compounds, Iodophores, Phenols

Based on Mode of Action:

• Act on Cytoplasmic Membrane: Quat. Ammonium compounds, Phenols, Biguanides, Alcohol
• Denaturation of Cellular Proteins: Aldehydes, Halogens
• Oxidation of Cellular Contents: Hydrogen Peroxide, Ethylene Di-oxide
• Alkylation: Formaldehyde, Beta propiolactone, Glutaraldehyde
• Act on Nucleic acid: Acridines

Disinfectants and their Mode of Action

Disinfecting Agent	Mode of Action	Examples
Alcohols	Membrane damage, protein denaturation, cell lysis	Ethanol, Propanol, Benzyl alcohol, Chlorobutanol
Aldehydes	React with amino acids, oxidizing agents	Formaldehydes, Glutaraldehydes
Biguanides	Membrane Disruption and protein coagulation	Chlorhexidine
Halogens	Interaction with thiol and amino groups → protein denaturation	Hypochlorite, Iodine, Iodophores
Oxidizing agents	Oxidization of cellular components	Hydrogen Peroxides
Quaternary ammonium compounds	Cell membrane damage, cytoplasmic leakage	Benzalkonium Chloride, Cetrimide
Organic acids esters	Cell lysis, membrane damage	Methyl, Ethyl, Propyl parabens
Alkylating agents	Alter cell metabolic activities	Ethylene Oxide

Disinfectants and their Uses

Disinfectants	Applications / Uses
Quaternary Ammonium Compounds	Skin Antiseptic, Eye drops preservative, Mouthwashes
Phenols	Hospital sanitization, soaps, lotions
Dyes	Skin and wound infection
Heavy Metals	Silver Nitrate (wounds), Arsenic (syphilis), Mercuric chloride (plants)
Ethylene Oxide	Sterilization of thermolabile items, surgical tools, catheters, gloves
Ethanol	Skin antiseptic, injection preservative
Iodine	Wound treatment, water treatment
Chlorine	Municipal water treatment, food industry

Factors Affecting Effectiveness of Disinfectants

• Population size / microbial load
• Nature of microorganisms
• Temperature
• pH of medium
• Concentration
• Presence of organic matter / inhibitors
• Presence of dead bacteria
• Other physical factors (humidity, water hardness)