Sterilisation and disinfection

Pregunta	Respuesta
Give 2 ways in which microbes have unwanted consequences for humans.	Disease Food spoilage
How can you reduce the undesirable effects of microbes?	Kill microorganisms or inhibit their growth
What has to be treated with sterile techniques?	Skin and other tissues, surgical instruments and gowns, wound dressings, solutions for injection and syringes, contaminated clothing and boots, animal habitats, e.g. kennels, stables, laboratory media and solutions.
What is the balance that has to be struck between the microbe and the item/area contaminated?	Between the effectiveness of the treatment agent being used against an infectious agent and its potential to cause damage to a patient or item under treatment.
What is starting to occur for	Chemotherapeutic agents acquired bacterial resistance Bacterial produce efflux pumps which can remove from cell
Define sterilisation.	The destruction/removal of all living cells, viable spores, viruses, viroids (nucleic acid infectious for plants) and prions (proteins infectious for animals, e.g. the agents of scrapie and BSE) from an inanimate object or habitat. Chemicals (sterilants) and physical means are available.
Define disinfection.	The destruction/removal or inhibition of microorganisms capable of causing disease from an inanimate object. Some vegetative cells and bacterial spores will remain following disinfection. Chemicals (disinfectants) and physical means are available.
Define sanitisation.	The reduction of a microbial population on an inanimate object to levels considered safe by public health standards.
Define pasteurisation.	The inactivation of human pathogens and non-pathogenic spoilage organisms from milk, beer, wine and other beverages. Most other vegetative cells will also be inactivated but spores will remain
Define antisepsis.	The destruction/removal or inhibition of micro-organisms from living tissue to prevent infection and disease. The chemicals (antiseptics) used are less toxic to tissue than disinfectants would be.
Define germicide.	A chemical able to kill microorganisms, e.g. bactericides, fungicides, viricides. (cf. bacteriostatic, fungistatic - chemicals able to inhibit growth).
What are the 4 main categories of physical antimicrobial agents?	Moist heat, Dry heat, Radiation Filtration.
Give 4 methods of moist heat.	Boiling/steaming Autoclaving Tyndallisation Pasteurisation
Give 2 forms of dry heat.	- Incineration - Hot air oven
Give 2 methods of irradiation.	Ultraviolet radiation Ionisation radiation
For boiling/steaming to ensure the death of all vegetative bacteria and fungi, viruses and eukaryotic spores, and some bacterial spores, exposure should be for?	At least 10 minutes at 100oC.
What does boiling/steaming not protect against?	Prions, e.g. BSE, and some bacterial spores, e.g. Clostridium tetani
Does boiling/steaming sterilise?	No
How can moist heat sterilise?	- Over 100 degrees C
How does autoclaving work?	Result of saturated steam under pressure in an autoclave / pressure cooker. 15psi (lb/inch2 ) provides 1210C at sea level and 15-20 minutes is sufficient under these conditions to destroy all microorganisms and spores
How should material suspected of having prions on be treated?	Soaked in 1N NaOH for 1-2 hours (but preferably overnight) prior to autoclaving to ensure destruction
How does the autoclave work?	- Boiling water is used to fill the autoclave chamber with saturated steam -> displacing the air present. - Chamber outlets are then closed but the saturated steam continues to enter, - Pressure and temperature rise - Required temperature and pressure have been attained, autoclaving is continued for the specified time. - The steam must be able to circulate freely and penetrate the items being treated in order to sterilise them. - Do not overpack the autoclave chamber and loosen bungs and lids. - Indicators are included with each autoclave run to ensure that the necessary conditions have been reached.
How does tyndallisation work?	- The material in its container is heated to 90-100oC (boiled / steamed) for 30-60 minutes to kill vegetative organisms and then incubated overnight at 37oC to enable any spores present to germinate. - The process is then repeated on each of two further days resulting in sterilisation.
Why is tyndallisation not used?	Time-intensive
What is the modern way of pasteurisation?	72oC for 15 seconds followed by rapid cooling
What is the D value?	Is the decimal reduction time, i.e. the time in minutes required to kill 90% of the organisms/spores in a sample at a specified temperature
What is the general trend of survival of bacteria with increased exposure?	Less survive
What is dry heat?	Dry heat oxidises the cellular constituents and denatures proteins
In a hot air oven, how can sterilisation occur?	Achieved in the absence of water using a hot air oven at 160 - 170oC for 2-3 hours.
What is hot air oven used for?	Glassware and metal instruments, and for products which would be ruined by water, e.g. waxes, powders and oils
How and when is incineration used?	Incineration can be considered as a means of destroying microorganisms if the contaminated object / material is disposable. This principle is also applied to the sterilisation of bacteriological loops for culture work in the laboratory.
When is ultraviolet radiation used?	Wavelength of approximately 260nm is capable of killing many types of vegetative microorganism since it is absorbed by the DNA causing thymidine dimers which inhibit replication and function
How is ultraviolet radiation used?	Sterilising agent is however limited by its inability to penetrate glass, water, films of dirt etc. The only real value is for sterilisation of the air and exposed surfaces in a room
How is ionisation radiation used?	Gamma radiation released by radioisotope (usually cobalt 60) decay has a much shorter wavelength and hence higher energy than UV radiation. High levels are lethal for all microorganisms and spores as a result of molecular ionisation, especially of DNA. The capability for deep penetration compared with UV radiation means that gamma radiation can be used for the sterilisation of sutures, dressings, and heat sensitive materials such as catheters, prostheses, disposable plastics
Where is ionisation therapy used?	This method would only be used in industry, it is clearly not suitable for routine veterinary hospitals.
How and why is filtration used?	Filtration is often used for the sterilisation of heat or radiation sensitive material such as injection solutions, antibiotic solutions, non-viscous culture media and pharmaceuticals.
What are the 6 main chemical antimicrobial agents?	Phenolics; Alcohols; Halogens; Quaternary ammonium compounds; Aldehydes; Sterilising gases; Miscellaneous
What and how is chlorhexidine used?	Used alone, this is only bactericidal but it is often combined with a quaternary ammonium compound to increase activity, e.g. Savlon, Hibiscrub. Such products are used for presurgical scrub, obstetric procedures, milking/diary operations. Kills by membrane damage and gelation of the cytoplasm
What and how is anionic detergents used?	Cleansing soaps (bars and liquids). Useful for removing superficial bacteria (from skin, floors, walls, utensils etc.) but they have little antimicrobial activity alone. They are therefore often combined with phenolics to increase bactericidal activity, e.g.Hexachlorophane in pHisoHex.
How is NaOH used?	Disinfection of stables / premises / transport
How is 3% hydrogen peroxide used?	Wound disinfectant and cleanser, mouth wash for stomatitis
What heavy metals are used and how?	Ions of mercury, arsenic, zinc and copper used to be used as germicides but they have largely been replaced by less toxic, more effective products. Dilute solutions of silver nitrate and mercuric chloride are however still in use as antiseptics. Ionic and colloidal silver though is an increasingly popular agents for use against skin infections and antibiotic-resistant bacteria.

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