Irradiation sterilization biological indicators

Strip

The strips are paper strips inoculated with Bacillus pumilus spores used to optimally verify radiation sterilization.

The strip is usually enclosed in a paper sachet, which must be placed inside the load and subjected to the sterilization cycle, during which the radiation hits the spores.

Once finished, the strip must be removed from the sachet and incubated for 7 days in Soybean Casein Digest Broth (TSB). Any cloudiness of the medium indicates bacterial growth and therefore sterilization failure. Broths with pH indicators are available which, by changing color with bacterial growth, allow a significant shortening of the incubation time to be validated.

Spore suspensions

Spores suspended in aqueous solution for particular needs, for example verifying the sterilization of thin or complex-structured medical devices.

Proceed by inoculating an aliquot of the suspension onto the sample and allowing it to dry. The object must then be packaged as usual and subjected to sterilization. At the end, the object must be incubated in culture broth to check for any bacterial growth.

It should be considered that the D-value indicated on the certificate refers to the tests performed on the suspension inoculated on paper strips and that the resistance could change significantly depending on the type of support on which the suspension is inoculated. In fact, spores can adhere to surfaces, forming thickenings in areas that appear porous or wrinkled at a microscopic level. This aspect is even more evident if you intend to inoculate the suspension in a liquid, whose effects on the resistance of the spore can be completely unexpected.