PCR confirms deletions in vaccine strains. Single colonies of vaccine or wild-type strains were used as templates for amplification of the guaBA (A) or sen (B) loci by PCR. (A) Lanes 1, molecular weight marker; 2, CVD 1208S; 3, 2457T; 4, CVD 1213; 5, J17B; 6, CVD 1215; 7, CCH060. The expected size of the guaBA band in the vaccine strains is ∼900 and ∼1800 bp in the wild-type strains using the primers Wu048 and Wu049. (B) Lanes 1, molecular weight marker; 2, CVD 1213; 3, J17B. The expected size of the sen band for CVD 1213 is ∼1400 and ∼1800 bp for J17B using the primers Wu060 and Wu061.