Ethylene oxide gas exposures. All EO exposures were performed with self-contained BIs with 106 spores of B. atrophaeus inoculated onto paper carriers (see Table I).
Unexposed controls: Three lots of EO BIs were incubated at 37 ± 2 °C in a conventional incubator to determine a baseline value for the time required
for BIs to exhibit nonsterile results (see Table IV). The average time for the first nonsterile BI in the three lots was 7.5 hours. Ninety-five percent of all BIs were nonsterile
in 10.2 hours. The incubation time between the first nonsterile BI and 95% nonsterile BIs was 2.7 hours; no delayed nonsterile
BIs were observed.
Table IV: Time-to-growth positive results for Bacillus atrophaeus biological indicators (BIs) exposed to ethylene oxide gas.
Calculated survival time exposures: The calculated survival time exposures were performed using three lots of 100 BIs. The average time for the first nonsterile
BI in the three lots was 18.2 hours. Ninety-five percent of all BIs exposed to these conditions were nonsterile in 21.3 hours.
The duration of incubation between the first nonsterile BI and 95 % nonsterile was 3.1 hours. This duration was approximately
15% longer than that found with the unexposed controls. No delayed nonsterile BIs were observed.
FDA RIT protocol exposures: Six lots of BIs were exposed to yield 30 to 80 BIs nonsterile per lot (see Table IV). The average time for the first nonsterile BI for the six lots tested was 21.96 hours. Ninety-five percent of all BIs exposed
to these conditions were nonsterile in 62.9 hours. The duration of incubation from the first nonsterile BI to 95% nonsterile
was 40.94 hours, which was approximately 13 times longer than that found with the calculated survival time exposures.
Table V : Time-to-nonsterile results for Bacillus atrophaeus biological indicators (BIs) exposed to chlorine dioxide gas.
Delayed nonsterile BIs were observed with two of the lots. Two BIs were observed in one lot and one BI was observed in the
second lot. The delayed nonsterile BIs grew out between 72 hours and 168 hours of incubation. Using the probability table
in Part I of this study, the authors projected that 66% of the nonsterile BIs would contain only one surviving CFU (1). However,
only 0.97% of the nonsterile BIs exhibited a delayed grow-out time.
The grow-out time results for all BIs exposed to EO gas are illustrated in the vertical scatter plots in Figure 1, Panel C. A graphical expression of these data appears in Figure 2, Panel C.