O.D. 600 nm readings to bacterial concentrations

Gerald Pier gpier at warren.med.harvard.edu
Tue Oct 10 13:38:56 EST 1995

In article <44rnn6$89o at news.internetmci.com>, "Gregory P. Harhay"
<gpharhay at internetmci.com> wrote:

> 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
> Thanks,
> Greg Harhay

One more thing to consider: Some organisms, like P. fluorescens, rapidly
adhere to glass or plastic culture vessels in some buffers, particularly
those lacking protein (i.e. saline, PBS, etc.).  So an OD reading followed
by dilutions and plate counts can be highly misleading as the organisms
stick to the dilution vessle walls quicker than you can pipette an aliquot
into the next vessel.  So I'd be careful and do my dilutions for plate
counts in several different buffers, including ones that have something
like 1% proteose peptone or BSA in them.

Jerry Pier

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