For paper carrier biological indicators, remove three specimens of the relevant biological indicators
1S (USP31) from their original individual containers. Disperse the paper into component fibers by placing the test specimens in a sterile 250-mL cup of a suitable blender containing 100 mL of chilled, sterilized
Purified Water and blending for
a time known to be adequate
1S (USP31) to achieve a homogeneous suspension.
It is not unusual for blending times of 15 minutes or more to be required for optimal recovery.
1S (USP31) Transfer a 10-mL aliquot of the suspension to a sterile, screw-capped 16- × 125-mm tube. For
Biological Indicator for Steam Sterilization, Paper Carrier, heat the tube containing the suspension in a water bath at 95
to 100
for 15 minutes (heat shock), starting the timing when the temperature reaches 95
. For
Biological Indicator for Dry-Heat Sterilization, Paper Carrier, and for
Biological Indicator for Ethylene Oxide Sterilization, Paper Carrier, heat the tube containing the suspension in a water bath at 80
to 85
for 10 minutes, starting the timing when the temperature
of the spore suspension
1S (USP31) reaches 80
. Cool rapidly in an ice-water bath at 0
to 4
. Transfer two 1-mL aliquots to suitable tubes, and make appropriate serial dilutions in sterilized
Purified Water, the dilutions being selected as calculated to yield preferably 30 to 300 colonies, but not less than 6, on each of a pair of plates when treated as described below. Where the biological indicator has a low spore concentration, it may be necessary to modify the dilution series and to use more plates at each dilution. Prepare a separate series of plates for each aliquot. Place 1.0 mL of each selected dilution in each of two 15- × 100-mm Petri dishes. Within 20 minutes, add to each plate 20 mL of
SoybeanCasein Digest Agar Medium 1S (USP31) that has been melted and cooled to 45
to 50
. Swirl to attain a homogeneous suspension, and allow
it
1S (USP31) to solidify. Incubate the plates in an inverted position at 55
to 60
for
Biological Indicator for Steam Sterilization, Paper Carrier, and at 30
to 35
for
Biological Indicator for Ethylene Oxide Sterilization, Paper Carrier and for
Biological Indicator for Dry-Heat Sterilization, Paper Carrier or at the optimal recovery temperature specified by the manufacturer. Examine the plates after 24 and 48 hours, recording for each plate the number of colonies; and
use
1S (USP31)the number of colonies
observed
1S (USP31) after 48 hours to calculate the results. Calculate the average number of spores per specimen from the results, using the appropriate dilution factor. The test is valid if the log number of spores per carrier at 48 hours is equal to or greater than the log number after 24 hours in each case. For
Biological Indicator for Steam Sterilization, Self-Contained, aseptically remove the
three carriers
1S (USP31) from the container, and proceed as directed for
Biological Indicator for Steam Sterilization, Paper Carrier.