Bob Friedel rfriedel at perrittlab.com
Wed Nov 10 07:53:29 EST 1999

When you design your experiment, you should also add disinfecting agent
neutralizers to the media when you perform your quantative recovery.  If
there is residual disinfectant in the recovery media you will produce false
negative results (i.e., the disinfectant residues will prevent the organisms
from repairing themselves and eliminate the possibility of producing visible

Disinfectants are usually neutralized in (3) ways:  1) chemical
neutralization (e.g., bisulfite or thiosulfate for clorinated compounds,
nonionics [Tweens 20 & 80] and lecithin for phenolics and acid preservatives
such as parabens), 2) dilution, 3) membrane filtration (i.e., physical

Robert R. Friedel
Quality Assurance Manager
Laboratory Research & Analysis Groups
Perritt Laboratories, Inc.
rfriedel at perrittlab.com

PEEBLESHS <peebleshs at aol.com> wrote in message
news:19991109103905.18106.00000924 at ng-cm1.aol.com...
> I am a sixth year pupil at Peebles High School, Scotland.  For my Sixth
> Studies Biology project I have been investigating the effects of different
> disinfectants on E.Coli, Bacillus Subtilis and Micrococcus Luteus.  I have
> altered the concentrations of bleach and Dettox and found that
> of less than 0.0001% bleach and 0.001% Dettox stimulate bacterial growth.
> anyone tell me why this happens?  I  found that a 5% phenol solution was
> effective against M. Luteus but ineffective against E.Coli.  E.Coli was
> very resistant to Rossopol - a washing up liquid.  Hydrogen peroxide was
> effective against all three bacteria.  Can anyone explain these findings.
I am
> also interested to know exactly how these disinfectants work - what do the
> terms anionic, cationic and non-ionic mean when applied to disinfectants?
> any other useful information.

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