Sterility techniques Flashcards
Define sterility.
Absence of viable micro-organisms.
What is the sterility assurance level?
The probability of survival of micro-organisms, no more than 1 micro-organism in 10^-6 vials.
Give five examples of substances that are required to be sterile.
Injections
Ophthalmic preparations
Implants
Dressings
Surgical ligatures
What are the five methods of sterilisation?
Steam sterilisation
Dry heat
Ionising radiation
Gas sterilisation
Filtration
Other methods include formaldehyde use with steam and UV light
What are the two types of heat sterilisation?
Dry heat sterilisation and moist heat sterilisation
When is dry heat sterilisation usually used?
For glassware, metal surgical equipment and non-aqueous thermostable liquids and
thermostable powders
What instrument is used for dry heat sterilisation?
A hot air oven with perforated
shelves to allow for heat & air flow, or heat sterilizing tunnels
What temperature and time should the oven reach for sterilisation?
160 degrees for 2 hours
170 degrees for 1 hour
180 degrees for 30 minutes
What must you remember when packing items into the oven?
Unscrew any lids to avoid bursting
Pack evenly throughout the oven
Containers should be sealed or covered
What are the conditions of the desterilisation of pyogenes?
250 degrees for 45 minutes
How does dry heat sterilisation work?
The dry heat sterilization process is accomplished by conduction; that is where heat is absorbed by the exterior surface of an item and then passed inward to the next layer. Eventually, the entire item reaches the proper temperature needed to achieve sterilization.
What are two advantages and two disadvantages of dry heat sterilisation?
Advantages:
Good for moisture sensitive products
Less damaging to glass and metal equipment
Disadvantages:
Drastic conditions are not tolerated by certain packaging
material e.g., plastics/rubber
* Not suitable for surgical dressings
* Does not penetrate as well as moist heat
* Natural moisture in fibres vaporises and causes
deterioration
How does moist heat sterilisation work?
It destroys micro-organisms by denaturing them with steam under pressure
What are the advantages and disadvantages of moist heat sterilisation?
Terminal sterilisation process for aqueous solutions or
suspensions
* Wide safety margin
* Kills bacteria and viruses
Disadvantages:
Only useful for thermostable products
* Can not be used for products with oily bases
* Water is essential
What are two gases used in gas sterilisation?
Ethylene oxide (CH2 )2O, and formaldehyde
How is the explosive nature of ethylene oxide reduced?
It is presented as a 10% mix with carbon dioxide or 8.6% mix with hydrochlorofluoro carbon) which has replaced fluorinated hydrocarbons (freons).
Why is a sterilising humidifier required when using ethylene oxide?
Organisms are more resistant to ethylene oxide in the dried state so there must be a minimum level of moisture.
What is the mechanism of action of gas sterilisation?
Gas sterilisation causes the alkylation of sulphydryl, amino, hydroxyl and
carboxyl groups on proteins and imino groups of nucleic acids.
What is the procedure for gas sterilisation?
Gas introduced after chamber evacuation
* Humidity required (pulsed steam)
* Gas mix exhausted and rendered harmless
When is gas sterilisation normally used?
Re-usable surgical instruments, certain medical,
diagnostic and electrical equipment, and the surface sterilization of powders. Alternative for radiation sterilisation.
Describe the sterilisation procedure involving ethylene oxide.
Firstly remove air using a vacuum.
Next add steam to reach the desired moisture (30% RH optimal anti-microbial activity).
Then sterilise by adding ethlyene oxide and set both the time and pressure.
After remove the vacuum and fit the air filter for air flushing.
Total air replacement.
What are three advantages and three disadvantages of gas sterilisation?
Few materials damaged minimal heat, minimal moisture
* Good penetration in porous loads will penetrate rubber & plastics
* Effective against all micro-organisms : bacteria, viruses, moulds
Disadvantages:
Gas is toxic and flammable
Costs are higher than dry heat
Residues need disposal
What are two advantages and two disadvantages of using radiation sterilisation?
Effective against a large number of bacteria, yeasts, moulds and some
viruses
* Terminal technique
* Used for surgical instruments, sutures, prostheses
* Dry pharmaceutical products (powders)
Disadvantages:
Not effective against some viruses
Cost, side effects
How does anti-microbial resistance decreases with ionising radiation?
Resistance decreases with the presence of moisture, dissolved oxygen or with elevated temperatures.
Describe the two types of radiation sterilisation.
Ionizing radiation is the use of short wavelength, high-intensity radiation to destroy microorganisms. This radiation can come in the form of gamma or X-rays that react with DNA resulting in a damaged cell. Non-ionizing radiation uses longer wavelength and lower energy. As a result, non-ionizing radiation loses the ability to penetrate substances, and can only be used for sterilizing surfaces. The most common form of non-ionizing radiation is ultraviolet light.
What size of membrane filters are normally used for filter sterilisation?
0.2-0.22 µm nominal pore
diameter are mainly used.
Describe a depth filter.
Made of asbestos & wood cellulose,
sintered glass, sintered ceramic; and not
absolutely retentive
Multiple layers, trap micro-organisms within
structure (used as pre-filter)
Fibrous material may shed
Describe a screen filter.
cellulose acetate
Screen filters are absolutely retentive
Suitable integrity tests required
Before use – check for defects
Should you prolong filtration?
No as bacteria may accumulate on filter
What bacterium can’t be collected by filters?
- Filter will not remove viruses
- Filter will not remove mycoplasms
- Form of bacteria with no cell wall
- Filters will not remove some G-ve “stunted forms”
What are some of the advantages of filter sterilisation?
Remove bacteria dead bodies (endotoxins)
Used for thermolabile products
What are some disadvantages of filter sterilisation?
Not suitable for suspensions
Not a terminal process
Sterility tests required so 7-14 day delay
Viruses and mycoplasms not removed
