This is a difficult question to answer, as the resistance of the BI, in
addition to other cycle parameters (i.e., %RH), will have an impact on how
quickly your indicators are killed at 700 ppm and 21 deg C. For example, we
have evaluated several manufacturerıs lots of VHP BIıs in the same cycle,
and have found differences in D-value of up to 14 minutes. Some of these
differences were due to varied D-values, the way the spores were harvested
and inoculated onto the stainless surface, and the cleanliness of the spore
crop. If the spore crop contains extraneous material during inoculation,
you may experience highly resistant lots or a tailing effect at longer
exposure times during your runs. This may be one explanation for what you
are currently experiencing. Finally, how are you measuring your VHP
concentration? Is it possible to see complete kill of 10e6 spores at the
parameters you indicated? Yes, but you would have to demonstrate this
through cycle development using an appropriate BI system.
Dr. Michael J. Miller
Senior Research Fellow
Manufacturing, Science and Technology
Eli Lilly and Company
Lilly Corporate Center
Indianapolis, Indiana 46285
317 651 6370
[log in to unmask]
On 5/23/06 4:01 AM, "David Keen" <[log in to unmask]> wrote:
> Hello Members,
> I have a query on performing a system D-value on an isolator system using VHP
> at a concentration of 700ppm at 21°C.
> Would you expect to see total kill of Geobacillus (population of 1.9x106) on
> stainless steel coupons after 35 mins exposure to the above concentration of
> This is the first system D-value we are performing using VHP. I am unsure as
> to whether we have a poor batch of manufactured BI's or if the bugs really are
> that resistant to VHP at the given Temp and concentration.
> Any comments or thoughts would be appreciated.
> Many thanks
> David Keen
> Tel: 01661 839266
> www.clinical-manufacturing.com <http://www.clinical-manufacturing.com/>
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