D value (Biological Indicator)

what’s the procedure to find the D- value for the biological indicator?
And I want to know how to calculate the survival and killing time .

Hello Mikry!

There are a couple of methods to calculate D-value. ISO 11138 has a more detailed explenation of theese methods, but I will briefly explain them here:

  • Survival curve method. It uses a direct enumeration of colony forming units (CFU) to measure how many spores survived at different exposure times.

  • Fraction negative method. It uses the Most Probable Number (MPN) method to estimate the survival population given a fraction of negative (no growth) BIs at different exposure times. This method has 3 variants in the calculation of the D value: Holocomb-Spearman-KArber method (HSK), Limited Holocomb-Spearman-Karber method (LHSK) and Stumbo-Murphy-Cochran method (SMC)

Survival time: no less than log (population - 2) * D-value

Kill time: not greater than log (population+ 4) * D-value

I hope this information is helpful!

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