limits to bacterial heat resistance?
Kevin G. Korth
kkorth at kcc.com
Thu Aug 17 13:20:13 EST 1995
Chris Michiels <chris.michiels at agr.kuleuven.ac.be> wrote:
>How heat resistant can I make an E. coli (or other bacterial) culture by
>consecutive rounds of selection, i.e. regrowing survivors of a partial
>What about bacterial spores? Can their heat resistance be boosted?
>What is the probability and the risk of such selections taking place
>during (mild) thermal food processing, and of more heat resistant
>pathogens entering the food chain? Or would such variants necessarily be
>cripple and have attenuated virulence?
>Opinions and references to relevant studies in the literature, please?
>Lab Food Microbiology
>Kard. Mercierlaan 92
Though I can't recall the references off the top of my head (and I am
too lazy to dig through my mountain of files just to respond to this
posting), historically, many studies have been published addressing this
very issue (especially with spores).
My personal opinion is that E.coli would only be able to develop heat
resistance to a certain point without vastly altering its internal
protein and membrane structure, which, I doubt could happen and still
maintain an E.coli genome.
Spores, on the other hand have been boosted in heat resistance to
phenominal levels. I recall reading of a B.stearothermophilus strain
that was capable of D-values in excess of 9 minutes at 121 C (autoclave
temperature) [most B.stearothermophilus have D-values between 1 and 2
minutes at that temp.]
If you are planning a study, make sure you include a large complement of
appropriate controls. There's nothing worse than making a phenominal
claim, only to get it blasted by poor experimental design.
One more thing. Never assume that a pathogen is crippled just because it
barely survived some treatment. The FDA would never buy such an
argument. To the FDA a pathogen is a pathogen, regardless of its
kkorth at kcc.com
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