Disinfection, Antisepsis and preservatives: types and choice of agents

Disinfection, Antisepsis and preservatives: types and choice of agents

This is the freeing of an article (inanimate objects) from some or its entire burden of live pathogenic microorganisms that might cause infection during its use, not usually including bacterial spores. Reduce to level acceptable for purpose e.g. harms neither human nor quality of products. Strong disinfectants are bacteriocidal but toxic to human tissues, and therefore suitable for disinfecting inanimate objects and the environment

Levels of action

Disinfection, Antisepsis and preservatives: types and choice of agents

High level-all microorganisms but not spore. Some may have good antispore activity and described as liquid chemical sterilants or chemosterilants. Intermediate-All vegetative including M.tuberculosis but may exclude some viruses and fungi, no sporicidal activity. Low level-destroy most vegetative bacteria, fungi and viruses not spore or resistant organisms.

Antiseptics and antisepsis

Antisepsis =destruction or inhibition of microorganisms on living tissue thus limiting or preventing harmful results of infection. Chemical applied to skin or mucous membrane must have antimicrobial activity and not be irritant or toxic to tissue. Mostly used to reduce micro before surgery or on hands to prevent spread of infection. They are either microbicidal or microbistatic

Preservatives and preservation

Preservatives are used for pharmaceuticals and other formulations to prevent microbial spoilage and to minimize risk of consumer acquiring infection when product used. Preservatives must limit microbial growth, kill any contaminants introduced in product and not be toxic.

  • Decontamination: treatment that renders an object or inanimate surface safe to handle
  • Bactericidal: an agent that kills bacteria
  • Bacteriostatic: an agent that inhibits bacterial growth
  • Germicidal: a chemical agent that kills or inhibits growth of microorganisms and is sufficiently nontoxic to be applied to living tissue (antiseptic)
  • Fungicidal: an agent that kills fungi
  • Viricidal: agent that stops viral replication and activity

Factors affecting choice of the agent

1. Property of chemical agent

How agent is influenced by concentration, temp, pH and formulationsTissue toxicity influence use as disinfectant, antiseptic or preservative.

2. Microbiological challenge-significant effect by type of micro and level of contamination (bioburden)

High bio burden-longer exposure or higher concentrationOrganisms: innate sensitivity/resistance; nosocomial infection

Microbiological challenge

  • Veg cell-Methicilin Resistant Staphylococus Aureus, Listeria, Campylobacter and Legionella
  • Causes of nosocomial infections esp Gram negative bacteria, Pseudomonas aeruginosa
  • Mycobacterium tuberculosis and other mycobacteria resistant to many bactericides. Care on equipment for respiratory investigations
  • Fungal spores may be more resistant than veg. fungal cell (but less than bacterial spore)
  • Bacterial spore can be resistant to even most active disinfectant! Can use aldehydes, peroxides or halogens but safety margins lower.
  • Viruses-without lipid envelop more resistant. Some highly infectious e.g. Ebola, HIV, Hepatitis 
  • A-need safe destruction and fast action.

G. Protozoa-Hydrogen peroxide used for Acanthamoeba (affecting contact lenses)H. Prions-Highly resistant to disinfectants and sterilization. Use of sodium hydroxide (1M), sodium hypochlorite (20,000ppm available chlorine) or mixture of 0.2%sodium docecyl sulphate, 0.3 NaOH in 20% n-propanol

3. Intended application-consider

  • Antagonism with medicinal preparation?
  • Close contact with broken skin?
  • Corrosive to instruments?
  • Adsorption of chemical effect on materials?

4. Environmental factors

  • Presence of organic matter such as blood, body fluids, pus, milk, food residues, colloidal proteins
  • Presence of ions

5. Toxicity of agent

E.g. toxic volatile substances-phenolics, formaldehyde, glutaraldehyde-can affect eyes, skin, respiratory system. Precaution-need to do regular sampling and analysis of atmosphere where disinfectants are used.

Differences between Antiseptic and disinfectant agents

Antisepsis: Is defined as destruction or inhibition of microorganisms on living tissues having the effect of limiting or preventing the harmful results of infection. 

Antiseptic: A substance that counters sepsis by destroying or inhibiting the growth of pathogenic microorganisms. Antiseptics are generally applied to living tissues in the form of wet dressings, creams, ointments or other substances that involve prolonged contact with the body.

Disinfection: is the process of removing microorganisms, including pathogens, from the surfaces of inanimate objects. 

Disinfectant: An agent that prevents infection by destroying or removing pathogenic microorganisms. The term is confined to substances used for the treatment of inanimate objects. In practice, both antiseptics and disinfectants are used to destroy or inhibit the growth of pathogenic microorganisms in the vegetative form.



Has a bactericidal action against most vegetative organisms at a concentration of 60% and 95%, but is not effective against bacterial spores. Evaporating lotion used for hand and skin cleaning, surgical treatment for various skin lesions. Prevention of bedsores and diminishing sweating (reduce temperature). Used as solvent in different pharmaceutical preparations. A concentration of 70% either alone or with chlorhexidine or iodine for disinfection of skin before surgical procedures

An antiseptic which is effective against a wide range of vegetative gram-positive and gram-negative bacteria, although it has no activity against acid fast bacteria, bacterial spores and some viruses. Chlorhexidine is used in disinfectant solutions, creams, gels and lozenges. It is also used in various concentrations for disinfection in the following conditions;

• Chlorhexidine 0.5% in 70% ethanol for the preoperative disinfection of the skin

• Chlorhexidine 0.05% solution in glycerin for urethral irrigation and catheter lubrication

• Chlorhexidine 0.02% solution for bladder irrigation

• Chlorhexidine 1% cream for use in obstetrics

• Chlorhexidine 0.01% as the diacetate for preservation of eye drops


A quaternary ammonium disinfectant that has bacterial activity against both gram-positive and gram-negative organisms. 0.5% solution for preoperative skin disinfection. Cetrimide 0.05% to 1% is used for the cleansing of polythene tubing and catheters, but time of immersion should not exceed 30 minutes. Cetrimide in higher concentrations of 15 to 35 is used in shampoos to remove scales in seborrhea. Cetrimide 1.5% with chlorhexidine gluconate 0.15% is often used as a general purpose disinfectant

Povidone Iodine /polyvidone iodine 

Acts by inhibiting enzymes essential to microbial metabolism. It kills on contact a broad spectrum of pathogenic bacteria, viruses, fungi, protozoa and yeasts. Skin antiseptics and germicidal skin cleansers. Disinfectant for wounds, abrasions and insect bites, Medicated spray for wounds, Antidandruff shampoos, Medicated adhesive plasters, Gargles and throat lozenges and vaginal gels and douches among others


Sodium Hypochlorite 

A solution 8% to about 18% of chlorine is prepared by absorption of chlorine in sodium hydroxide solution to give sodium hypochlorite. Sodium hypochlorite solutions release chlorine gas which kills most pathogenic organisms at neutral ph, Rapid disinfection of hard surfaces, Disinfection of food, Disinfection of dairy equipment and babies’ feeding bottles, Solutions containing up to 0.05% of available chlorine are suitable for use on skin and wounds.

Glutaral (Glutaraldehyde) 


Glutaral is an effective disinfectant against vegetative forms of gram-positive and gram-negative bacteria. It is also effective against acid-fast bacteria, bacterial spores, some fungi and viruses. A 2% aqueous solution of Glutaral buffered to pH 7.5-8.5 (the ambient pH for activity) is used for the sterilization of endoscopic instruments, thermometers and rubber or plastic equipment that cannot be sterilized by heat

Cresol and Soap Solution 

Cresol and soap solution BP (Lysol) is an old preparation which is still widely used in East Africa as a general disinfectant for hospital and domestic use. Cresol and soap solution is effective against a wide range of organisms, but its activity is reduced in the presence of organic matter. The bactericidal activity of cresol and soap solution varies with the soap used. Linseed and castor oil soaps give the highest values and oleic acid the lowest. 

It has further been verified that higher values are obtained with coconut oil. In addition to its use as a general disinfectant in hospitals, cresol and soap solution is widely used in commercial disinfectants. Because it is clear when diluted with water, its use is an advantage in the sterilization of surgical instruments, since cleanliness can be identified with speed and ease.


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