Principle of disinfection
Disinfection lectures
• Principle of disinfection
• Individual disinfection processes
• Water and wastewater disinfection
(w/disinfection kinetics)
• Air disinfection and disinfection on
surfaces
• Disinfection on infectious solids (biosolids)
Definitions
• Sterilization: A process intended to remove
or destroy all viable forms of microbial life,
including bacterial spores.
Definitions
• Disinfection: The destruction of pathogenic
and other kinds of microorganisms by
physical and chemical means.
• Disinfection is less lethal process than
sterilization because it destroys most
recognized pathogenic microorganisms,
but not necessarily all microbial forms
such as bacterial spores.
Definitions
• Preservation: The process by which
chemical or physical agents prevent
biological deterioration of substances.
Definitions
• Sterilizer: An agent that destroys or
eliminates all forms of microbial life in the
inanimate environment, including all forms
of vegetative bacteria, bacterial spores,
fungi, fungal spores, and viruses.
Definitions
• Disinfectant: An agent that frees from
infection, usually a chemical agents but
sometimes a physical one, such as x-rays
or ultraviolet light, that destroy disease or
other harmful microorganisms but may not
kill bacterial spores. It refers to substances
applied to inanimate objects.
Definitions
• Sanitizer: An agent that reduces
contaminants in the inanimate
environment to level considered safe as
determined by Public Health Ordinance, or
that reduces the bacterial population by
significant numbers where public health
requirements have not been established.
Definitions
• Antiseptics: An agent that opposes sepsis,
putrefaction, or decay by preventing or arresting
the growth of microorganisms.
– Antiseptic products are applied on or in the living
body of humans or other animals.
• Antibiotics: an organic chemical substance
produced by microorganisms that has capacity
in dilute solutions to destroy or inhibit the growth
of bacteria or other microorganisms.
– It is usually used as a chemitherapeutant and must be
low in toxicity while effective against microorganisms.
The target sites of antibiotics
Common sterilizers and disinfectants
• Sterilizer
– Most heat (>121 oC)
– Dry heat (> 160 oC)
– Ionizing radiation
• Disinfectant
– Physical
• Ultraviolet radiation
• Hydrostatic pressure
– Chemical
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Alcohols
Phenols
Quaternary ammonium compounds
Glutaraldehyde
Iodine and iodine compounds
Chlorine species (free chlorine, chloramines, and chlorine dioxide)
Ozone
Mechanisms of sterilizers and disinfectants
• Sterilizer
– Moist and dry heat: protein denaturation, enzyme
inhibition, RNA and DNA breakdown
– Ionizing radiations: single or double-strand breakage
in DNA
• Disinfectants
– Ultraviolet radiation: thymine dimers, various
photoproducts (5,6-dihydroxy-dihydrothymine, TDHT,
pyrimine-(6-4)-pyrimidone,…)
– Chemical disinfectants: protein denaturation, enzyme
inhibition, breakdown of nucleic acids
Mode of action of (chemical) disinfectants
• Adsorption on the microbes’ surface
• Diffusion through the surface
• Binding to the vulnerable sites (e.g.
plasma membrane, cytoplasmic proteins,
nucleic acids, and so on)
• Disruption of the vulnerable sites
• Injury and death of the microbes
Structure of viruses
Structure of bacteria
Structure of bacterial cell walls
Structure of fungi
Structure of fungal cell wall
Structure of algae
Components of algal cell walls
• Cellulose
• Silica or calcium carbonate or
polysaccharide
Structure of bacterial spores
Surface structure of bacterial
endospores
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Exosporium: a thin protein cover
Spore coat: layers of spore-specific proteins
Cortex: loosely cross-linked peptidoglycan
Core: core cell wall, cytoplasmic membrane,
cytoplasm, nucleoid, ribosomes, and others
• Remarkable physical barrier against sterilization
and disinfection
– Survive up to 150 oC with dry heat
– Extremely resistant to ultraviolet, strong acid and
bases, and chemical disinfectants
Structure of Giardia cysts
Surface structure of Giardia cysts
• An inner membrane
• A thick (0.3 µm) outer filamentous portion
• Filaments
– 7-20 nm in diameter
– Protein and a unique carbohydrate (ß(1-3)-N-acetylD-galactopyranosamine)
– Strong interchain interaction and tightly packed
meshwork
• Remarkable physical barrier against most
chemical disinfectants
Surface structure of Cryptosporidium oocyst
Surface structure of Cryptosporidium oocyst
• Glycocalyx
– 82 % carbohydrate, 17 % protein, and trace fatty acid
• Outer oocyst wall
– Multilaminate glycoprotin, lipid, and lipid conjugates
• Central lipid layer
• Inner oocyst layer
– Cross-linked glycoprotein
– Outer and inner zone
• Remarkable physical barrier against most
chemical disinfectants
Structure of Helminth eggs (Ascaris)
Surface structure of Helminth eggs
(Ascaris)
Surface structure of Ascaris eggs
• Outer surface: protein and filamentous
fibers
• Outer limited membrane
• Chitinous zone
• Inner limited membrane
• Considerable physical barrier against most
chemical disinfectants
Factors in antimicrobial processes
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Target microorganisms
The media to be treated
The intended use of the media
Presence of interfering materials in the
media
Antimicrobial products
• Regulated by EPA
• 5000 antimicrobial products (1997) with
256 antimicrobially active ingredient
– 19 % sanitizers
– 80 % disinfectants
– 1% sterilizers
Selection criteria
(chemical antimicrobial agents)
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Antimicrobial efficacy
Corrosivity
Chemical hazard
Environmental concerns
Stability
Biocidal spectrum
Corrosivity
Chemical hazard
Environmental concerns
Stability
To be continued