What is the difference?
Does it affect viability?
If there is a difference in measurement, is it significant?
Dear Issac,
No, it makes no difference whether you make optical density readings at 595 or 600 nm – the choice of which to use (or other wavelengths) really depends on the colour of your growth medium and the size and shape of the bacterial cells.
I have worked with pseudomonas and with E. coli, so I have stuck to LB and KB media with readings at OD600. However, the colour of the medium might affect the readings, so it is important to check sterile media and a culture with a scanning spectrophotometer to find the best wavelength to record cell density. Cell size and shape will also affect light scattering, so once again, if you are growing something different, you should also scan your culture. Finally, just to make sure, you should determine the OD for a range of cell densities and make sure that there is a good linear relationship between OD and cell numbers which have been determined by microscopy or by plating for viable cells.
Andrew
