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[Andras]

Dear All,
I have ran into a problem: I am doing a version of the plaque assay, and my dilution factors do not usually coincide with the number of fluorescent focus units I observe. Sometimes I do see a trend of 10-fold decrease as the dilutions go down, but especially at lower dilutions it does not work out -I'm usually getting a few positives in the lowest dilution sets as well, which will obviously mean that the PFU is extremely high if I calculate it from this dilution.
Another problem sometimes comes up when I work with concentrated stocks: the dilution-series from 10e-1 - 10e-9 sometimes are just not enough: I still have about 20% of cells infected on the lowest dilution...

All this, of course, means that my PFU values calculated from the different dilutions will wary 2-3 orders of magnitude. Which is confusing.
How and what should I change? None of the manuals, books or articles are discussing the practical parts of data analysis, and all their examples are nice and clear-cut.
Unlike my experience...
Thank you for your help.