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 o C) –Dry heat (> 160 o C) –Ionizing radiation Disinfectant –Physical Ultraviolet radiation Hydrostatic pressure –Chemical 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 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 o C 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-acetyl- D-galactopyranosamine) –Strong interchain interaction and tightly packed meshwork Remarkable physical barrier against most chemical disinfectants

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 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) Antimicrobial efficacy Corrosivity Chemical hazard Environmental concerns Stability

Biocidal spectrum

Corrosivity

Chemical hazard

Environmental concerns

Stability

To be continued