M2: Sterilisation and disinfection Flashcards
Define sterilisation
Removal/inactivation of all micro-organisms from an article including bacteria, viruses, fungi and spores
Define disinfection
Removal/inactivation of some micro-organisms from an article usually excluding bacterial spores
Define antiseptic
Substance which destroys or inhibits growth of micro-organisms which can be applied onto living tissue such as open wounds or abrasions
Define asepsis
The state of being free from living organisms
What are the 4 main methods of steralisation
- Heat
- Irradiation
- Gas
- Filtration
What is moist heat
This is more effective in sterilisation than dry heat and requires temperatures above 100 degrees which is attained by raising the pressure of steam in the autoclave vessel which is saturated with water vapour
When is dry heat used
- Incineration is used for pathological waste materials
- Red heat and flaming are types of dry heat
- Hot air sterilisers
- Microwaves are not reliable for sterilisation
What is irradiation
When ionising radiation (gamma, x-rays and accelerated electrons) are used for commercial sterilisation of single used items
What is gaseous sterilisation
When ethylene oxide (penetrative and non-corrosive gas) is used for sterilisation of one use items
What is filtration
This is a sterilisation technique used to exclude bacteria from fluids (0.22um = pore size filter) - most viruses can pass through
Give an example of a biological sterilisation indicator
Bacillus spp; the strip will be cultured after sterilisation and if there is growth, the process has not been successful
Give an example of a non-biological sterilisation indicator
- Externally calibrated thermocouple linked to a time monitor
- Autoclave tape and Brownes’ tubes show that apparatus has reached the correct temperature
- TST indicator strips
What are the 5 main methods of disinfection
- Moist heat
- UV radiation
- Gasses (formaldehyde gas)
- Filtration
- Chemicals
What are the classes of disinfectants
- Alcohols (isopropanol and ethanol)
- Aldehydes (glutaraldehyde)
- Biguanides (chlorhexidine)
- Halogens (hypochlorites, iodophors, providone iodine)
- Phenolics
- Peroxygenated compounds
- Surface-active agents
What is more sensitive to disinfection
Gram-positive bacteria are more sensitive to disinfection than gram-negative; mycobacteria and fungal spores are highly resistant; enveloped or lipophilic viruses are relatively sensitive (HIV) and hydrophilic viruses are less susceptible, Hep B is resistant
What are the three main sources of infection in the dental surgery
- Patients suffering from the infections disease
- Patients in the prodromal stage of infections
- Individuals who are carriers of pathogenic micro-organisms
What are the three main ways of infection transmission in the dental surgery
- By direct contact of tissues with skin or body fluids
- By droplets containing infectious agents
- Via contaminated instruments which have not been rendered safe for reuse
What are the pros and cons of autoclave sterilisation
This is steaming under pressure
Strengths = low running costs Weaknesses = apparatus is expensive, rusts dental instruments
What are the pros and cons of chemiclave
No longer used; various microbiocidal substances at high temperatures usually in vapour form
Strengths = doesn't rust dental instruments, cycles cannot be interrupted Weaknesses = long cycle time, vapours may be harmful, machine needs careful maintenance, chemicals involved are expensive
What are the pros and cons of hot air ovens
Hot air sterilisation
Strengths = very cheap to run Weaknesses = long cycle, not reliable even when fitted with circulatory fans, damages instruments, sterilisation cycles can be interrupted
