Biological indicators for steam sterilization
General
Steam sterilisation (or autoclaving) is carried out by introducing saturated water vapour under pressure. In addition to the temperature effect itself, the presence of saturated water vapour is essential to kill microorganisms, their destruction being due to irreversible denaturation of cell components.
Product description
Biological indicators used to test steam sterilisation are microorganisms (spores of Geobacillus stearothermophilus, originally from ATCC 7953), prepared on filter paper as carrier material and packed in primary packaging consisting of transparent plastic film and paper which is steam-permeable.
The steam indicators fulfil the specifications in EN ISO 11138-3, i.e. an initial microbial count of at least 105 CFU/unit, a D-value at 121°C of at least 1.5 min. and a Z-value of at least 6°C.
Use
Typically, autoclaving is carried out with a sterilisation time of a minimum of 15 minutes, at 121°C and pressure of 2 atmospheres, or a minimum of 3 minutes, at 134°C and 3 atmospheres. Items sterilised with steam are typically not sensitive to heat, e.g. simple surgical instruments, handpieces and angled pieces, reusable medical equipment, hollow surgical equipment and textiles.
The efficacy of the sterilisation process is improved if the air is removed from the chamber before the introduction of steam. Achieving a vacuum can be difficult. Residual air hampers the penetration of steam into cavities in instruments, etc. The use of biological indicators is therefore recommended both for routine testing and in connection with validation/revalidation of the equipment.
For non-validated equipment and for equipment not being operated at the ‘overkill’ setting, routine testing every month is recommended, and, for validated equipment, 4 times a year or after 200-400 cycles. 'Overkill' means that the process has been conducted under conditions exceeding the minimum requirements for the sterilisation process in question.
Product range
The steam indicators are supplied in packs of 3 or 6. Subsequent culturing at Statens Serum Institut can be ordered separately.
Article-
number |
Product |
| 75621 |
6 unit pack without culturing, 105 CFU per unit |
| 75620 |
3 unit pack without culturing, 105 CFU per unit |
| 75622 |
6 unit pack without culturing, 106 CFU per unit
(for validation) |
| 75669 |
Culturing of 3 units |
| 75670 |
Culturing of 6 units |
In addition, a subscription scheme is available for monthly or quarterly testing with 3 or 6 units per pack. All subscribers receive deliveries twice a year, at 6-monthly intervals.
This scheme is suitable for small clinics (dentists, specialists, etc.) requiring regular testing.