Sterilisation and Disinfection Flashcards
Define Sterilisation
The removal or inactivation of all micro-organisms from an article including viruses, bacteria and their spores’ and fungi and their spores
Define Disinfection
Removal or inactivation of some micro-organisms from an article
Define Antiseptic
Substance which destroys or inhibits the growth of micro-organisms - can be applied to living tissue
Define Asepsis
State of being free from living organisms
Define cleaning
Soil removing process - removes high proportion of micro-organisms present, usually prior to disinfection/sterilisation
What are the 4 main methods of sterilisation
- Heat
- Irradiation
- Gas
- Filtration
What are some influencing factors that affect sterilisation by heat
- Temp
- Time
- Number of organisms
- Species and spore-forming ability of the micro-organisms
- Nature of contaminated materials
Is moist heat or dry heat better for sterilisation
Moist heat
What are the conditions required to use moist heat for sterilisation
- Temp>100C
- Raising pressure of steam in pressure vessel (Autoclave)
- Steam must be saturated and dry must not contain water droplets
What are different methods to apply dry heat sterilisation
- Incineration
- Red Heat
- Flaming
- Hot Air Steriliser
- Microwave Ovens
When can you use hot air sterilisers
For materials that can withstand high temps for prolonged times and are likely to be affected by contact with steam
What occurs in the red heat sterilisation method
Points of forces held in flame
What temps and times are the minimums for dry heat sterilisation
160C - 60mins
170C - 40mins
180C - 20 mins
What temps, pressures (in lb/in^2) and times are the minimums for dry heat sterilisation
121C - 15lb/in^2 - 15 mins
126 - 20lb/in^2 - 10 mins
134 - 30lb/in^2 - 3 mins
How is Irradiation sterilisation carried out
- Ionising radiation including gamma rays, x rays and accelerated electrons
What is irradiation often used for
Commercial sterilisation of single use items e.g. plastic straws
Describe an example of how Gaseous sterilisation can be carried out
Ethylene oxide - highly penetrative and non-corrosive - used for commercial sterilisation of single use items
Describe filtration sterilisation
Useful to exclude bacteria from fluids - 0.22um. pore size filter, excludes more bacteria but most viruses can pass
What are sterilisation indicators
Used to determine whether sterilisation has occurred e.g. inside autoclave
Describe how biological sterilisation indicators work
Usually cultures of Bacillus spp - after use the strips are cultured in media and any growth is indicative of sterilisation failure
Name some non-biological examples of sterilisation indicators
- Externally calibrated thermocouple linked to a time monitor
- Autoclave tape and Browne’s tubes show apparatus show apparatus reached correct temp
- TST indicator strips (temp., steam, time)
What are the 5 main methods for disinfection
- Moist Heat
- Ultraviolet Radiation
- Gases
- Filtration
- Chemicals
Describe the basic features of the moist heat disinfection method
- First choice
- No toxic residues
- 70-80C for a few mins kills most
- NB - boiling water won’t sterilise surgical instruments
Describe the basic features of the ultraviolet radiation disinfection method
- Poor penetrating power
- Mercury lamps used in treatment of air, water and surfaces
Name a gas used for gaseous disinfection and what this method would be used for
- e.g. formaldehyde gas - used for rooms and complex heat sensitive equipment
Where is the filtration disinfection method used
Widely applied in the removal of micro-organisms to critical sites e.g. operating theatres
What affects the activity of chemical disinfectants
- Concentration
- No., type and location of micro-organisms
- Temp and pH of treatment
- Presence of extraneous material e.g. organic substances
What classes of disinfectants are there
- Alcohols
- Aldehydes
- Biguanides
- Halogens
- Phenolics
- Peroxygenated compounds
- Surface-active agents
Name some alcohol disinfectants
- Isopropanol
- Ethanol
Name some aldehyde disinfectants and when are these used
Glutaraldehyde
Used for equipment that cannot be sterilised or disinfected by heat - broad spectrum of activity
Name a Biguanide disinfectant and when are these used
Chlorhexidine
Used for disinfection of skin and mucous membranes
Name some types of halogen disinfectant
Hypochlorites and iodine containing complexes (iodophors and povidone iodine)
What are phenolic disinfectants used for
General purpose environmental disinfectants
When are peroxygenated compound disinfectants used
For surface disinfection - good anti-microbial properties
What kinds of surface active agents are there
Anionic, cationic, non ionic, Amphoteric detergents
Are gram positive or negative bacteria generally more sensitive to disinfectants
Gram positive are more sensitive
What spore producing microbes are highly resistant to disinfectants
Bacterial spores - highly resistant
What type of viruses are quite sensitive to disinfectants
Enveloped or lipophilic viruses (HIV)
What type of viruses are not very susceptible to disinfectants
Hydrophilic (Polioviruses and other enteroviruses)
When should and instrument be sterilised
Any instrument that comes routinely into contact with blood, saliva or tissue that are surgically breached should be sterilised, any other should be disinfected
What in the GD practice is disinfection generally used for
- Decontamination of surfaces
- Treatment of spillages
- Decontamination of areas known to be grossly contaminated
- Decontamination of non-surgical instruments
- Decontamination prior to sterilisaiton
- Decontamination of dental unit water supplies
What are the 3 main sources of infection in the GD practice
- Patients suffering from the infectious disease
- Patient in the prodromal stage of certain infections
- Individuals who are carriers of pathogenic micro-orgnaisms
What are the 3 main ways of infection transmission in the GD practice
- Direct contact of tissues with skin or body fluids
- By droplets containing infectious agents
- Via contaminated instruments that haven’t been rendered safe for re-use
What are the advantages and disadvantages of using the Autoclave for sterilisation
Advantage: Running costs low
Disadvantages: Apparatus is expensive and it rusts the dental instruments
How do Chemiclaves work
Various micro-biocidal substances at high temps usually in vapour form
What are some advantages and disadvantages for using the chemiclave for sterilisation
Advantages: Does not rust dental instruments; cycles cannot be interrupted
Disadvantages: Long cycle time; vapours may be harmful; Machine needs careful maintenance; Chemicals involved are expensive
What are the advantages and disadvantages of hot air ovens
Advantages: Very cheap to run
Disadvantages: long cycle; not reliable even when fitted with circulatory fans; Damages instruments; sterilisation cycles can be interrupted
