Blood bag sterilization verification: How do biological indicators Ensure that sterilization Effects Meet standards

In blood bag sterilization validation, biological indicators ensure the sterilization efficacy meets standards through the following methods:

1. Selecting appropriate microbial strains
   Choose strains with greater resistance than potential contaminants in sterilized products for different sterilization methods. For example, in moist heat sterilization, Geobacillus stearothermophilus spores (e.g., NCTC 10007, NCIMB 8157, ATCC 7953) are most commonly used as biological indicators. Their D-values range from 1.5 to 3.0 minutes, with a viable spore count of 5×10⁵ to 5×10⁶ per strip/vial. These spores should be completely inactivated under 121°C for 19 minutes.

2. Determining spore resistance
   Biological indicator validation requires testing spore resistance under actual sterilization conditions, including assessing spore purity and quantity. During validation, the microbial load in biological indicators should exceed daily contamination levels and demonstrate higher resistance to ensure sterilization process safety margins.

3. Scientific placement of biological indicators
   Prior to sterilization, position biological indicators inside or at representative locations of sterilized items to ensure full exposure to sterilization conditions. For example, in terminal sterilization processes, indicators should be distributed across different areas of the sterilization chamber while avoiding direct contact with sterilized products.

4. Standardized incubation and observation
   Post-sterilization, incubate biological indicators under appropriate conditions. Bacterial spore indicators typically require 24 hours to 7 days at 37°C or 56°C. Results are interpreted through system changes:

   • Color change (e.g., purple to yellow) indicates microbial growth (sterilization failure)
   • Stable color indicates successful sterilization
     Some indicators use fluorescence or alternative detection methods.

5. Biological indicator challenge testing
   Validate sterilization programs by demonstrating achievement of pre-determined microbial kill times.

   • For overkill method validation: Use Geobacillus stearothermophilus with D₁₂₁°C >1 and cycle F₀ >12
   • For probability-of-survival method: Indicator heat resistance must exceed product bioburden resistance, incorporating historical bioburden data with safety margins.

6. Control setup and evaluation
   Include positive controls in challenge tests to confirm adequate inoculum placement and absence of interference. Evaluate results to verify logarithmic reduction values meet requirements, ensuring product microbial survival probability (PNSU) <10⁻⁶.