Each biological indicator (BI) that is manufactured contains a known number of microorganisms (also referred to as spores). In order to confirm that the BI actually contains the expected number of spores, an individual will need to perform a population assay. In USP <55>, this is referred to as Total Viable Spore Count. This particular chapter provides a detailed description of the steps to take when performing a population assay – from sample size (at least four test samples) to creating a dilution series, heat shock time and temps, and incubation time and temps.
For each dilution series, calculate the yield to be between 30-300 colonies on a plate. 1.0 mL of each dilution is then placed into two petri dishes, and swirled with 20 mL of agar. These plates are then incubated at a species-appropriate temperature for at least 48 hours. From there, a calculation is performed to figure out the average number of spores per unit.
Let’s talk biological indicators!
Talk with one of our experts to get your questions answered and see how we can help you solve your BI pain points.