O.D. 600 nm readings to bacterial concentrations

Douglas B. Kell dbk at aber.ac.uk
Wed Oct 4 03:04:21 EST 1995

In article <44rnn6$89o at news.internetmci.com> "Gregory P. Harhay" <gpharhay at internetmci.com> writes:
>I need to convert my O.D. 600 nm "absorption" readings of pure
>cultures of Pseudomonas fluorescens (ATCC 13525) and 
>Brochothrix thermosphacta  (ATCC 11509) suspended in buffer
>to an estimate of their concentration in the buffer. Are there
>any good references out there? ATCC is no help
>Greg Harhay

Just to be (not in fact) pedantic, please drop the "absorption" or
even absorbance. OD is NOT absorbance (but scattering). Rule of
thumb for bugs says (in the Beer-Lambert range, typically up to OD
0.6) that 1 OD = 0.5 mg dw/ml. Every bug is different, and
it depends on where the cuvette is in the spec and the optics 
thereof - you have to make your own calibration curve. The ref I
usually cite is Mallette, M.F. (1969) Evaluation of growth by 
physical and chemical means. in Methods in Microbiology (ed. 
JR Norris & DW Ribbons) Vol 1, 521-566. Academic Press, 


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