BCG vaccine: an investigation of colony morphology from four different strains after their introduction as seed for vaccine preparation in four production laboratories

Four collaborating BCG production laboratories had each prepared vaccine from four different BCG strains. In this laboratory the morphology of colonies cultured from samples of the 16 vaccine lots thus available was examined, and it was found that changes monitored in earlier small-scale experimental reconstructions had also occurred during some of the full-scale production procedures, in accordance with prediction. In particular, a minority population carried by the Danish BCG strain had replaced the original majority when this strain had been employed as seed for the production of vaccine by the British procedure. Similarly, a minority carried by the Japanese strain had replaced the original majority when this strain was introduced as seed into the production procedures in the United Kingdom and France. Serial subcultures made in this laboratory showed, in accordance with previous experience, that the changes that had occurred in the Japanese strain could be completely reversed by serial subculture as a surface pellicle on Sauton medium.