Background: In February 2004, FDA approved a supplement to our biologics license for Carticel, autologous cultured chondrocytes, to use the BacT/ALERT microbial detection system as an alternative to the compendial sterility test for lot release. This article provides a roadmap to our approval process. The approval represents more than 4 years of development and validation studies comparing the Steritest compact system to the BacT/ALERT microbial detection system.
Methods: For this study, freshly cultured chondrocytes were prepared from a characterized cell bank. Microbial isolates were prepared from either American Type Culture Collection (ATCC) strains or from in-house contaminants. For each test condition, a suspension of chondrocyte cells and test organisms was inoculated into both aerobic media (SA standard adult culture bottles, FA FAN, tryptic soy broth) and anaerobic media (SN standard adult culture bottles, FN FAN, fluid thioglycollate media) and tested for sterility using the Steritest compact system (Millipore, Bedford, MA, USA) and the BacT/ALERT microbial detection system (bioMerieux, Durham, NC, USA). Negative control bottles were inoculated with chondrocytes and no microorganisms. All bottles were incubated for 14 days and read daily. Bacterial growth was determined by either visual examination of Steritest canisters or detection of a positive by the BacT/ALERT system. A gram stain and streak plate were used to confirm positive bottles and negative bottles after 14 days.
Results: The detection of a positive by either the Steritest compact system or the BacT/ALERT system was summarized for each organism in each validation study. Data generated from studies reducing the incubation temperature from 35 degrees C to 32 degrees C improved detection times in the automated method compared with the compendial method. Other improvements included the use of FAN aerobic and anaerobic media to absorb the gentamicin contained in the culture media of prepared chondrocyte samples. Chondrocytes alone did not generate positive results in either the compendial method or the automated method.
Discussion: Data from validation studies support the use of the BacT/ALERT microbial detection system as an alternative sterility test for Carticel.