Test organism
Spores of Bacillus atrophaeus (Bacillus subtilis var. niger) (ATCC 9372; NCIMB 8058; CIP77.18) are used for validation and routine monitoring of the performance of sterilizers and sterilizing processes employing dry heat at sterilizing temperatures, typically at 160°. For routine monitoring, the D-value shall not be less than 2.5 minutes.
Identification
The biological indicator organism complies substantially with the morphological, cultural and biochemical characteristics of the strain of Bacillus atrophaeus ATCC 9372; under microscopic examination it consists of Gram positive rods of width 0.7 μm to 0.8 μm, and length 2 μm to 3 μm, the endospores are oval and central and the cells are not swollen; when incubated aerobically in appropriate media at 30° to 50° growth occurs within 24 hours and similar inoculated media incubated concomitantly at 55° to 60° show no evidence of growth in the same period; agar colonies have a dull appearance and may be cream to brown to orange-colored; when incubated in nutrient broth it develops a pellicle, and shows little or no turbidity.
Biological Indicator
The indicator used is Biological Indicator for dry-heat sterilization, paper carrier. It is a defined preparation of viable spores made from a culture derived from a specified strain of Bacillus atrophaeus, on a suitable grade of the paper carrier, individually packaged in a container readily penetrable by dry heat, and characterized for predictable resistance to dry-heat Sterilization. It has a particular labeled spore count per carrier of not less than 10^4 and not more than 10^8.
Dry heat at temperatures greater than 220° is frequently used for Sterilization and depyrogenation of glassware and glass containers. In this case, demonstration of a 3-log reduction in heat resistant bacterial endotoxin can be used as a replacement for biological indicators.
Also see: Types of Biological Indicators
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