What the Heck is a Steam Integrator?

Everyone knows that one of the first rules to successful biology is sterility. How many times have you used media that was not properly sterilized and caused delays in your lab process?

Are you sure the instruments that you just you took out of the autoclave are actually clean?

Well, if your lab uses autoclave tape as an indicator of a proper sterilization run in the autoclave, let me introduce you to steam integrators and the difference between the two.

Autoclave tape is basically a Class 1 Indicator; it is designed to react to one or more sterilization variables, typically temperature. There are also Class 4 chemical indicators, which are designed to react to two or more variables of sterilization (e.g., time and temperature). Typically, these are paper strips that are placed inside instrument packs or printed on the inside of instrument pouches.

My favorite is the Class 5 integrating indicators. They look similar to Class 4 chemical indicators but use steam-sensitive chemicals — layered between paper and aluminum foil — that melt during the sterilization cycle. As the chemicals reach the melting point, they move along a paper-wicking strip. The time it takes to move the chemical into the “pass” or “accept” area of the strip approximates the time it is necessary for bacterial spores in spore strips to be killed, with an added margin of safety (additional time).

Class 5 integrators are designed to react to all three critical variables of sterilization — time, temperature, and steam. An integrator will confirm that steam has penetrated a pack for a certain amount of time at a certain temperature. Class 5 integrating indicators must indicate exposure that is comparable to a biological indicator — 121°C or 250°F for longer than 16.5 minutes.

You can buy a pack of 100 Class 5 Steam Integrators for around 50 dollars. I prefer to use “Comply SteriGage” from 3M. If you really care about sterility, you should be using a class 5 steam integrator with your autoclave runs.