ash at umich.edu ash at umich.edu
Fri Jun 25 12:50:23 EST 1999

Something is not right.  The Klett vs. time curve which started me on this was
published in J.Bact. 181:3649-3657 (Federle, et. al.)  This is Group A
Streptococcus in an unidentified Todd-Hewitt preparation. Stationary phase is
entered at Klett 100.  Koch, A.L. tells us this is Abs = 0.2.  Having grown
equivalent strains in three different commercial preparations of Todd-Hewitt, I
know they typically grow up to Abs = 1.5 or so.  I am being pedantic to some
degree, but I can mathematically define absorbance and transmission; I am in the
dark still with the definition of a Klett. The curves in this particular paper are
useful, they show the relative rates of growth of three strains, I cannot compare
them directly to my own curves though.

Why do not we use nephelometry to measure the concentration of our
bacterial suspensions?  From what I understand, it is more sensitive
at the lower concentrations, and hence might be useful in generation
lag phase curves.  Nephelometry measures the intensity of scattered light
at a right angle to the sample and the light source.  Scattered light
is proportional to the intensity of the light source (not so in a turbidometric
set up measuring transmission - light source, sample, detector in a linear

Andrew Heath
Research Associate
University of Michigan
Infectious Diseases

: According to A.L. Koch in "Manual of Methods for General Bacteriology", 
: ASM Press 1981, p 197, 500 Klett units corresponds to an Absorbance
: of 1.0.

Thanks for a textual reference, alas that text is not in the University of
Michigan in Ann Arbor's Library.

: Raymond Cox
: Institute of Biochemistry
: Odense University, Denmark

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