Experimental bacterial growth curves with OD600 in the y-axis typically show rate of growth until a stationary/plateau phase is reached. Theoretical growth curves with the number of cells in the y-axis additionally show the death phase, where the number of cells declines.
Can the spectrophotometer distinguish between dead or living cells at the plateau phase, for example if they scatter light differently? or can this only be known from additional viability assays such as stains?
Hello Paniz Sehat Niaki
The OD at 600nm will give you a count that will include both the live and dead cells. The microbial cells do not absorb the light but scatter the light depending mostly on their size and shape. Not all of the scattered light can reach the detector. Dead microbial cells and cell debris also scatter the light, meaning that the absorbance value does not correlate directly to viable microbial cells. The amount of light that reaches the detector depends on two parameters namely, the number of scattering microbial cells (density) and the dimension of the microbial cells (size and shape).
Spectrophotometer will not be able to distinguish between dead or living cells. You will have to carry out additional assays. I have attached a paper for your reference.
https://journals.asm.org/doi/pdf/10.1128/jb.30.2.193-206.1935#:~:text=Within%20a%20short%20time%2C%20living,1922)%20who%20used%20congo%20red
Best.
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