cheap probe to detect log growth

John Gentile yjgent at
Sat Dec 2 21:36:50 EST 2000

Your sensor has to be able to tell the difference between living and dead
organisms. Also the flask needs to be agitated constantly.

Many years ago we had an instrument that was supposed to produce a growth
curve in a small vial of TSB inoculated with urine. When it worked it was
impressive, but there were times when the germs just outsmarted the machine.
L-forms of E. coli, slow growing organisms, Yeast, some Gram pos's all gave
inaccurate results. The yeast was interesting since it did seem to grow, but
was too heavy to stay in the broth and sunk to the bottom where the sensor
could not read it.

Our blood culture instrument measures pH by a pH disk in the bottom of the
culture vial. It's not a real growth curve, just a measure of the pH and
once it goes acid it will stay there when the organisms die off.

John Gentile                            Rhode Island Apple Group
yjgent at                         Past President, Publicity Chairman
 "I never make mistakes, I only have unexpected learning opportunities"

> From: Michael Witty <mw132 at>
> Organization: University of Cambridge, England
> Newsgroups: bionet.microbiology
> Date: Sat, 2 Dec 2000 15:36:52 +0000
> Subject: cheap probe to detect log growth
> Dear All, I am convinced there must be a better way of finding the log
> phase of growth (for example of a conical flask of E. coli) than
> repeatedly taking 1ml samples and putting them in a spec.
> My ambition is to have a cheap detector with a probe consisting of a
> light source and photoresistor which can be dangled into my flask and
> record data continuously.
> But I am a biologist not an electrical engineer.  Does anyone share
> my ambition?  Or know how I can make this happen?  Mike.

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