Some biological, biochemical and morphological changes and their correlations in selected BCG vaccine strains

Abstract

Changes in the biological, biochemical and morphological properties of three BCG strains, Copenhagen BCG 1331 and two of its derivatives, Praha BCG 725 SH and Praha BCG 725 SAS, were studied and correlated. These changes were caused by chemical (culture media) and physical factors (freeze-drying). The highest immunizing potency and the highest lipid content were displayed, both prior to and after freeze drying, by the Danish strain. Long-term cultivation of the Danish strain on different media in Prague resulted in a decrease of its immunizing potency and lipid content. Both of the Czechoslovak strains derived in this manner, BCG 725 SH and BCG 725 SAS, differed mutually by their immunizing potency, lipid content and percentage of intact cells. The immunizing potency and lipid content of these two strains were in inverse proportion; so were the immunizing potency and percentage of intact mycobacteria. The experiments suggested that substantial changes develop after physical action (freeze-drying) only in strains being maintained on rich culture media. Freeze-drying changed the relationship between immunizing potency and lipid content into a direct one in both of the Czechoslovak strains. The relationship between immunizing potency and percentage of intact mycobacteria remained inverse. In BCG 725 SH, total lipids and immunizing potency decreased and the percentage of intact cells increased after freeze drying. In BCG 725 SAS on the other hand the immunizing potency increased, lipids remained on a stable level and the percentage of intact cells decreased. The substantial changes in these parameters induced by freeze-drying subsequently returned to the original values irrespective of whether the strains had undergone a number of freeze-drying procedures or had been passaged directly after a single freeze-drying run. An essential effect was thus only produced by the first freeze-drying, and the changes appear not to be stable.