What are the five qualities of a good disinfectant?

Answer 1

DisinfectionDecontamination of laboratory benches, furniture, equipment and other materials requires the use of chemical disinfectants. Their activity is related to the following factors:

• concentration
• pH
• contact time
• humidity
• temperature
• presence of organic matter

Choosing a DisinfectantMicroorganisms present a range of resistances to chemical disinfectants and no single disinfectant is effective in all situations. Consider the following points when selecting a disinfectant:

• type of microorganisms, numbers and presence of spores
• physical situation (surface type, suspension, etc.)
• contact available between disinfectant and microorganisms
• possible interaction between disinfectant and materials
• contact time allowable
• concentration

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Preparing Working DilutionsFollow the manufacturer's recommendations for dilution of concentrated disinfectant.

• Prepare fresh dilutions daily
• Use clean, dry containers
• Use clean water for dilutions

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Common DisinfectantsChlorine Compounds

Generally used in the form of sodium hypochlorite.

• Effective against a wide variety of microorganisms (vegetative bacteria and viruses). Preferred disinfectant for HIV and hepatitis viruses.
• Use at 0.1% as a general disinfectant.
• Less suitable in the presence of organic matter (such as blood). Concentration must be increased to retain action (0.5%).
• Effective between a pH range of 6-8.
• Strength decreases on standing (make fresh solutions daily).
• High concentrations corrode metal surfaces, and bleach and damage fabrics.

Alcohols

Ethanol (80% v/v ethyl alcohol) or 2-propanol (60-70% v/v iso-propyl alcohol) solutions are used to disinfect skin and decontaminate clean surfaces.

• Effective against fungi, vegetative bacteria, Mycobacterium species and some lipid-containing viruses.
• Not effective against spores.
• Most effective at 70% in water.
• May swell rubber or harden plastics.
• Do not use near flames due to flammability.

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Iodine

Iodine vapour is highly toxic and is absorbed through the skin

Iodine is used in aqueous or alcoholic solution.

• Rapidly effective against most microorganisms.
• Usually diluted to 1% w/v free iodine, optimum pH neutral to acid.
• Not suitable in the presence of organic matter.
• Stains skin and may cause irritation.
• Dilute in alcohol for washing hands, or use as a sporicide.
• Prepare dilutions daily.
• Most commonly used for skin disinfection and decontaminating clean surfaces.
• Decomposes when heated above 40ºC.
• Do not use on aluminum or copper.

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Formaldehyde

Precautions are required when handling formaldehyde (refer Australian Standard 2508.6.026)

Formalin is 37% w/v formaldehyde gas in water.

• Active against most microorganisms.
• 13% v/v formalin is a good decontaminant (but has an irritating odour).
• 8% v/v formalin in 80% v/v alcohol is effective against vegetative bacteria, spores and viruses.
• Does not corrode stainless steel.
• Use to disinfect equipment such as centrifuges or biosafety cabinets.
• Formaldehyde can be used to disinfect rooms, cubicles and safety cabinets: THIS PROCEDURE MUST BE PERFORMED BY NATA ACCREDITED PERSONNEL ONLY.
• Generated by heating paraformaldehyde suspended in silicone oil to 160ºC.
• Use 5 grams formaldehyde per cubic metre of space to be decontaminated.
• Requires relative humidity between 70% and 90% (humidity can be raised by evaporating water into the room).
• Formaldehyde can react with free chlorine to produce toxic gas. Remove hypochlorite solutions and hydrochloric acid from spaces to be decontaminated.
• Neutralise with ammonia following decontamination.

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Glutaraldehyde

Glutaraldehyde is known to cause dermatitis and Asthma

Glutaraldehyde is commercially available as 2% w/v aqueous solution which must be made alkaline to "activate" (e.g. by addition of 0.3% sodium bicarbonate).

• Active against vegetative bacteria, spores, fungi and many viruses.
• Less irritating than formaldehyde, but may cause dermatitis. Wear protective gloves when handling materials which have been immersed in glutaraldehyde.
• Discard if turbid.
• Also available in stable glycocomplexed form which does not require addition of alkaline buffer.

Chorohexidine

Chlorhexidine as chlorhexidine gluconate is dissolved in 70% alcohol.

• Use as antiseptic. Apply alcoholic chlorhexidine to the skin in the event of accidental contamination.
• Effective against Gram-positive organisms and HIV.
• Not recommended as a general disinfectant.
• Not active against sporulating bacteria or non-lipid-containing viruses.
• Active in pH range 5.5 - 8.0.
• Incompatible with soap and anionic detergents.

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Hydrogen Peroxide

A concentration of 3% w/v generally used for disinfection.

• Active against a range of microorganisms.
• Fungi, spores and enteric viruses require higher concentration.
• No toxic end-products of decomposition.
• Do not use on aluminum, copper, zinc or brass.

Phenolics

Synthetic phenolics (clear soluble fluids) can be used as general disinfectants in the laboratory.

• Active against bacteria and lipid-containing viruses.
• Not active against spores and non-lipid-containing viruses.
• Active in presence of organic matter.
• Use for disinfecting floors, walls, benches and other furniture.

Quaternary Ammonium Compounds

Quaternary ammonium compounds are positively charged (cationic) surface-active disinfectants.

• Effective against Gram-positive bacteria and lipid-containing viruses.
• Not recommended as general disinfectants (they have a narrow antibacterial spectrum).
• Inactivated by proteins, soap and anionic detergents.

Activity of Different Types of DisinfectantsToxicity AgainstDisinfectantPhenolic CompoundsHypochloritesAlcoholsFormaldehydeGlutaralIodophors

Answer 2

(i) It kills all pathogenic bacteria at room temperature.

(ii) It is inexpensive.

(iii) It is non-toxic.

(iv) It provides protection against contamination during transportation and storage.

Answer 3

1. non-corrosive

2. inexpensive

3. not harmful to humans and other forms of life

Answer 4

arsenal are the best