Interesting thread. I have also seen the widespread practice of folks
incubating media fill units at temperature x followed by temperature y. It's
hard to precisely determine cause and effect regarding recoveries and
temperature pulse, particularly when they are within the same (mesophilic)
Does this make sense as a compromise: Namely, divide the units. One-half are
only incubated at temperature x for 14 days; the remaining one-half are
incubated at temperature y for the 14 days. All things being equal, this
would eliminate the argument about a given temperature causing a deleterious
effect on the recovery potential of microbes. Of course, we also know that it
is highly unlikely the contaminants will be equally distributed in the units
to start with.
A technical services study could substantiate whether FDAs thesis is borne
out, i.e., group A (all units) is incubated at x for 7 days followed by y for
7 days whereas group B is incubated at x (half the units) and y (remaining
half of units), each for 14 days. I'll share my pre-study bias.
Since we are shooting for zeros and this an all-or-none test, I'd settle on
the temperature (range) that causes the highest number of positive units, and
worry less about proving that strain A (i.e., "bug of the month") is being
potentially suppressed by exposure to temperature x, y, x/y or y/x (within a
14 day timeframe). It could be that time is more important than temperature
in maximizing recovery, particularly when comparing two temperature setpoints
(20-25C and 30-35C) within a common (meophilic) range. I think that sterility
test results from the Australian authorities have proven this fact, e.g.,
incubation over 28 days yields higher number of contaminated units than 14
days within the meophilic range.
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