Disinfection
Why Disinfect?
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To reduce or eliminate exposure risk
 Biohazard waste disposal
 Spill cleanup
 Routine surface decontamination
To eliminate contamination risk
 Preparation of microbiological media and
supplies
 Preparation of work area for cleanliness-critical
tasks
Resistance to Disinfectants
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Prions
Bacterial spores
Coccidia
(Cryptosporidium)
Mycobacterium
Nonlipid viruses (Hep A,
Polio)
Fungi
Rickettsiae, Chlamydiae
Vegetative bacteria
Lipid-containing viruses
Classes of Disinfectants
Chlorine
 Iodine
 Alcohol
 Phenolics
 Quaternary Ammonium
 Glutaraldehyde
 Hydrogen peroxide
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Factors Influencing Efficacy
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Surface/Topography – uneven, cracked or pitted
surfaces especially wooden surfaces can hide
microorganisms and are difficult to disinfect
Temperature - elevated temperatures may
enhance germicidal action but also evaporation
rate
Relative Humidity – many disinfectants have
optimal relative humidity range for maximum
effectiveness
Water Hardness – some disinfectants may be less
effective when diluted in hard water
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Organic Load
 Blood, sputum, milk, bedding, feed,
manure
 Proteins physically protect and stabilize
many microorganisms
 Adverse effect on action of many
disinfectants
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Concentration
 In most cases, the higher the
concentration, the more rapid the kill
 Consider potential damage to surfaces or
tissues
 Reducing concentration to avoid
damage will require additional contact
time
 Ultimately, disinfectant will no longer
be active enough to be useful
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Contact Time
 Disinfectants should be effective with a
short contact time
 Manufacturer’s recommended contact
time may be unrealistic under in-use
condition
 Contact time may depend on the method
of application
 For surface applications, loss by
evaporation may require frequent
applications to achieve contact time
Some Other Factors
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Dirt, grease and oils – all can protect the organism
and will repel water based disinfectants
Types of microbes present – spores, vegetative
cells, viruses
Dried spills (from media, buffers) can protect
microorganisms from contact with the disinfectant
pH
Age of the product/solution
Method of application (spray vs. wipe)
Rate of application
Storage condition