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I am working on gram positive bacteria for which OD was reported and some reported mcfarland value. I am new to microbiology. i want to confirm the only thing that matters is cfu. please reply for what shoul I prefer thank you.

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  • $\begingroup$ I think you need to give more info. An example would be great. A key question is whether the McFarland value refers to the apparent absorbance at 600nm, or the apparent % transmission (at 600nm) or (and I'll bet it is this one) the cell density in CFU/ml. E.g, a McFarland value of 3 means that the cell density is 3 x 10-to-the-power-of-eight cells/ml (but it does not imply an OD of 3). Apparent OD may be converted to McFarland values, see en.wikipedia.org/wiki/McFarland_standards. Finally, I say apparent OD because the measured effect is due to light-scattering,not 'true' OD. $\endgroup$ – user1136 Dec 19 '18 at 11:12

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