Determining genetic stability in Clostridium tetani vaccine strains

To develop a method for improved assessment of the genetic stability of bacterial vaccine strains, we applied next-generation sequencing to a Clostridium tetani model strain (including inter- and intra-lab replicates) and other strains. Data were processed to determine (gain or loss of) gene copy numbers. Strains could easily be distiguished based on gain/loss of prophage-like and CRISPR/Cas genes. We found that the model strain has multiple copies of the plasmid carrying the gene coding for tetanus toxin as well as several other genes. Data were reproducible within and between laboratories. The limit of detection of our method is an order of magnitude better than that of the pulsed-field gel electrophoresis (PFGE) currently used during manufacturing. This approach may part of an approach to reduce animal testing during vaccine manufacturing. Overall design: 14 samples,including the model A strain and three other strains, with inter- and intra-laboratory replicates for the model strain.