Disinfection; Preservatives and factors affecting the choice of agent


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

Antisepsis =destruction or inhibition of microorganisms on living tissue thus limiting or preventing harmful results of infection
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 formulations
Tissue 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 concentration
Organisms: 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.


Disinfection; Preservatives and factors affecting the choice of agent Disinfection; Preservatives and factors affecting the choice of agent Reviewed by gafacom on February 05, 2020 Rating: 5

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