Chemical methods of sterilization and disinfection Flashcards
Chemical methods
- Antiseptics - Skin, mucous membranes
- Disinfectants
- Environment
- Types: Alcohol, Chloride and chlorine-based compounds, Iodine-based compounds, Aldehydes, Peroxide based compounds, Surfactants (tensids), Acids and alkalis, Miscellaneous
- Ideal disinfectant: Wide spectrum, Quick, Irreversible effect, Long lasting, Contamination has no negative effect, Not toxic, water-soluble, Not corrosive, cheap, Not flammable, Easy to use, odorless, Stable, Cleans, No environmental problems
Alcohols
- ethyl-, isopropil-alcohol,
- mixture of ethyl-and isopropyl-alcohol etc.;
- disinfection based on water extraction
- greater effect on the Gram-negative vegetative bacteria
- used in combination with other disinfectants
- used for skin disinfection
Chlorine based compounds in general
- at room temp: yellow-greenish, suffocating, oxic gas
- water soluble, forms hypochloric acid (HOCl) which dissociates into HO and active chlorine
- active chlorine: strong germicide effect, penetrates cell membrane, destroys cellular enzyme
- highly volatile -> increased temp reduces capacity, over 30-40oC no capacity
- organic materials decrease capacity
- corrosive - metal, rubber, plastic
Sodium hypochloride
- very common
- 5-15% active chlorine and 1-3% sodium hydroxide
- NaOH gives stability to active chloride BUT corrosive on metals, skin irritation
- conc. 3-5% -> vegetative form of bacteria and all viruses BUT not destroy: acid fast bacteria, spores (over 15% conc), fungi, parasites
- pH range 5-7 -> chlorine is most volatile
- suppressed by the presence of organic materials
- storing conditions: in dark, closed containers, low temp
- DO NOT MIX: NH3, formaldehyde
Calcium hypochlorite
- solid
- CaHOCl + CaCl + Ca(OH)2–> chlorinated lime (bleach powder)
- > white, greyish, chlorine smelling, crumbling, hydroscopic powder, active chlorine: 25-35%
- use: 2% - virus, bacteria vegetative form/ 20% - spores
- no effect against fungi and parasites
- disinfection of wells, other water resources and surfaces
Kloramin-T / Toluol
◦ whitish powder with chlorine odor
◦ Active chloride: min.25%
◦ Effect: bactericide, virucide, High cc sporocide too,
- No effect against fungi and parasites
Sodium dichloro-isocyanurate (NaDCC or SDIC)
◦ colourless, water-soluble solid
◦ strong chlorine odour
◦ 1 tablet to 10l water
◦ Effect is 30sec, in the presence of organic/inorganic contamination too
◦ Effect: bactericide, virucide, High cc sporocid and fungicid too
Iodine based compounds
• Iodophores→ iodine + organic substrate (surface active materials) which contain also
◦ + phosphoric acid→ solubilising the iodine (detergent)
◦ +buffers→↓pH
◦ +polyvinyl-pyrolidine→ bind up to 30% of iodine
• Disinfection: Iodine released from complex→ oxidizes function groups of germs
• Iodine content of the commercially available iodofores: 0.5-1.7%
• dark brown -light yellow (depends on active iodine content)
• Surface friendly, powerful cleaning effect, pH3-4
• Iodophors: Iodine complexed with an organic substrate (Incosan-W, Wescodyne, Iosan)
‣ 3-5% destroys vegetative forms of G+ and G-germs/ 6-10% sporocide effect/ 10% fungicidal effect
• Povidone Iodine - Betadine (pavidone-iodine)
Iodine based compoundes Pros and Cons
- advantage: Bactericidal, viricidal, and fungicidal
- disadvantage: Occasional skin sensitivity, Partially inactivated by organic debris, Less residual activity than chlorhexidine, Poor sporicidal activity
Aldehydes
- Efficient, broad spectrum
- CHO- radicals → destroy cell wall
- Germicidal
- Formaldehyde
- Formalin
- Glutaraldehyde
- Other aldehyde based disinfectants: paraformaldehyde, glioxal, lysoform etc.
Formaldehyde
◦ at room temp: characteristically stinky
◦ Excessively irritant
◦ suffocating, cough evoking
◦ colorless gas which attacks all mucosal membranes
Formalin
- commercially available form of formaldehyde
- 35-37% water solution of the gas that contains further 10% methylalcohol and contaminants (formic acid, acetone etc)
- disinfection of surfaces
- water solution
- in form of gas
Disinfection with watery solution of formaldehyde (formalin)
◦ usual concentration: 1-6%
◦ Temp dependencies
‣ optimum: 30-35oC
‣ below 20oC quick decrease
‣ below 13oC no disinfection capacity
‣ over 35oC quick volatilization, quick decrease
◦ pH optimum: pH2.4-4.0
◦ organic materials do not hinder its disinfection efficiency
◦ concentrations: vegetative forms: 1-3%, spores: 6%, acid-fast: 6-10%, moulds: 5%, viruses: 3-5%
Disinfection with formaldehyde gas
◦ generation of gas from the watery solution:
‣ by heating
‣ by aerosol generators
‣ by oxidizing materials (e.g. potassium permanganate)
◦ microclimatic requirements:
‣ more than 20 oC is needed
‣ optimum humidity: 80-90%
◦ optimum gas concentration in the air: 0.1-0.2%
◦ WARNING: in 7-73% conc formaldehyde forms EXPLOSIVE MIXTURE WITH AIR!
◦ Formaldehyde gas can be neutralized with ammonium gas
Glutaraldehyde
◦ Light yellow, slightly acidic liquid (25% Glutaraldehyde + ethanol)
◦ Activation with base (opt.pH8), Stable for 2weeks
◦ 2% bactericid, sporocid, virucid, fungicid
◦ Not paraziticid!
◦ Not corrosive,
◦ Toxic Sodium bisulfitede activates
Other aldehyde based disinfectants
- paraformaldehyde: white, crystallized, formaldehyde stinking powder, used for gas disinfection of smaller stables.
‣ For 1m3 of stable air
• 10g of paraformaldehyde should be added to
• 30ml of water
• then first 0.1g sodium hydroxide and
• Afterwards 20g potassium permanganate should be added to the solution - glioxal
- lysoform etc.
Hydrogen peroxide
◦ colorless, odorless, aggressive, mildly acidic liquid, which decomposes with high speed;
◦ due to its speedy decomposition and strong corrosive effects the pure form is not used for disinfection;
◦ tensids (surface active materials) stabilize and lessen the corrosive effect;
◦ these compounds might be used for disinfection of utensils in 3-10% conc.
Peroxy-acids
- combo of hydrogen-peroxide and several organic acids
- > mostly formic and acetic acids
- commercially available peroxy-acids also contains phosphoric-acid and stabilizers
Peracetic-acid
◦ aggressive fluid with vinegar-like odour;
◦ widely used in food industry
◦ in production of SPF animals—> wide antimicrobial effect (at low concentration) :
—> vegetative form: 0.2%, fungicide + sporocid: 0.4%, coccidiotic: 0.4%
◦ quick decomposition after use - Liner disinfection
◦ over 30oC quick evaporation
◦ simultaneous use with alkalis is forbidden!
Surfactants
- surface active agents
- water/alcohol solution of these compounds reduce the surface tension of liquid surfaces dirty with fatty/greasy materials
- help to remove them
- enhance the efficiency of other disinfectants
- anion-active tensids
- cation-active tensids
- non-ionic tensids
- ampho-tensids
- anorganic acids
- organic acids
- alkalis
Anion-active tensids
◦ alkyl benzene sulfonate, alkil - sulphates, alkan - sulphates, some soaps etc.;
◦ strong lipoid solvent capacity;
◦ no disinfectant capacity;
◦ Deactivates the cation active tensids!
Cation-active tensids
◦ Cetil-trimethil-ammoniumbromide, benzalkoniumchloride etc.;
◦ Sterogenol, Bradophen-H, etc.;
◦ Substances with disinfection capacity over pH3;
◦ they reduce the surface-activity of cell membranes and increase the permeability
◦ hard water reduces their efficiency
Non-ionic tensids
◦ TWEEN-80 is the most known tensid of the group
◦ in solutions they do not dissociate into ions;
◦ mild disinfection capacity;
◦ they are often used in combination with other disinfectants;
Ampho-tenids
- these compounds contains both acidic and alkalic groups in the molecule
- in acidic surrounding they behave as cation-active tensids;
- in basic surrounding they act as anionic-tensids
Anorganic acids
◦ (nitric-, hydrochloric-, sulphuric-and phosphoric-acid);
◦ due to strong corrosive effect today are not used
Organic acids
- (formic-, lactic-, malonic-, glutaric-, propionic-acid)
- they are used in combination with other disinfectants to obtain enhanced virucidic and sporocidic activity;
- salts of the propionic-acid or its combination with fumaric-, sorbic-acid, mono- and diglicerides are used for disinfection of grains
Alkalis
◦ disinfection is based on the strong alkalic pH they provide;
◦ Calcium hydroxide—> slaked lime - Whitewash
◦ sodium-, potassioum-hyroxide: were used by the dairy industry;
—> hot solution in 2-4% concentration: bactericide, virucide
—> in 6% concentration: sporocide
—> strong corrosive effects
Gaseous disinfectants
- at room temp in gas-state
- ethylen-oxid
- beta-proprionlactone
- methyl-bromide
Ethylen-oxid
◦ sweetish-ether like substance;
◦ boiling point at 10.70C;
◦ good penetration: paper, cellophane, plastic containers;
◦ MOA: it attacks the sulphohydril-, amino-, carboxyl- and hydryl-radicals of proteins;
◦ strong bactericide, sporocide, virucide effect;
◦ at 450mg/l conc it kills all microbes;
◦ labour safety considerations:
-> inflammable, explosive
-> inhalation: headache, nausea, mucosal irritation
-> agriculture: textile and other containers, feed
Beta-propionlactone
- used for gas-sterilisation
- poisonous inhalation
Methyl-bromide
- good insecticide
- min. 15oC, 300g/m3
