Population Verification

Woodhouse Laboratories offers more than standard presence/absence testing of biological indicators. We are also offer Biological Indicator Population Verification tests. Population verification is useful for:

  • Verifying that your biological indicator meets manufacturer’s claims of the population inoculated on the carrier
  • Initial autoclave verification - determine lethality rates and D-values
  • Research projects - Need to know the quantity of bacterial spores remaining after a sterilization cycle? Population verification provides quantitative data.



The Biological Indicator Population Verification test determines the number of spores on a biological indicator (BI) and is used to enumerate survivors from a sterilization process to determine lethality rates and D-values. A count ensures the count recovered meets manufacturer’s claims of the population inoculated on the carrier.

Population enumeration is important because it provides quantitative data, whereas a BI sterility test only provides growth/no growth results.

These are tested in accordance with USP <55> Biological Indicators – Resistance Performance Tests or manufacturer’s instructions.


Method Description

When performing Biological Indicator Population Verification testing, BIs are macerated using sterile glass beads. The macerate is then heat shocked, and the suspension is diluted to yield colonies in the range of 30–300 colony-forming units (CFU) and then plated. Other methods can be used as required. All results are compared against an untreated spore strip or BI control.


Please contact us for pricing information.