Isoenzyme analysis of typhoid-Shigella and Escherichia-Shigella hybrid vaccines and their parental strains.

Isoenzyme analysis can be used to measure phenotypic changes and to characterize bacterial strains. The use of isoenzyme analysis to characterize bacterial hybrid vaccine strains that were prepared for human vaccination is described in this report. The hybrid vaccine strains were two lots of Salmonella typhi-Shigella sonnei vaccine, two lots of Escherichia coli-Shigella flexneri vaccine, and their parental strains. The two lots of S. typhi-S. sonnei hybrid vaccine had only 5 of 11 reactive isoenzymes in common. The lot of S. typhi-S. sonnei hybrid vaccine that protected human volunteers in a clinical trial also had a greater degree of relatedness to the parental strain, S. typhi Ty21a, than the nonprotective lot. The two lots of E. coli-S. flexneri vaccine were more similar in terms of their isoenzyme profiles. There were colonial isolates from both lots that had identical isoenzyme profiles. The results also indicate a greater degree of homogenicity between Shigella spp. and E. coli than between either of these species and Salmonella spp. The data also show more isoenzyme activity associated with the nonpathogenic bacteria than with pathogenic isolates. Isoenzyme analysis is a rapid and specific assay that can be used to evaluate bacterial vaccine organisms and to establish isoenzyme profiles associated with vaccine immunogenicity and efficacy.