Sterilization
Wet
In moist conditions microorganisms germinate and grow vegetatively. It is relatively easy
to kill them in a wet environment. A laboratory autoclave often is set up for thirty minutes
at one atmosphere of pressure or 121 ° C. When solids are present, e.g., soymeal
in the culture medium, the exposure time should be increased to allow heat to penetrate
into any solid clumps.
Dry
Absence of moisture encourages the formation of bacterial endospores that are a means
of preserving the organisms. These spores are roughly 1000 times more resistant to heat
than vegetative cells. The sterilization of such materials as glass pipettes uses not a steam
autoclave but an oven. Typical conditions are several hours at 200 ° C.
Antifoam oil is essentially dry and should be sterilized either at higher temperatures or for very
prolonged periods in a steam autoclave.
29-Oct-96