Table 2.

Attenuating deletion mutations in S. flexneri 2a strain CVD 1207 and S. flexneri 3a strain CVD 1211

Vaccine strain(s)MutationPhenotype
S. flexneri 2a and 3a (CVD 1207 and CVD 1211) ΔguaB-A Inactivates de novo synthesis of GMP, GDP, and GTP
 Decreased invasion rate (27)
 Decreased intracellular growth (27)
ΔvirGicsA)Inactivates VirG
 No intracellular and intercellular spreading (2)
Δsen::Ptac-ars Inactivates enterotoxin ShET2 (25)
High-level resistance to arsenite
 Allows the identification of vaccine strains
 Permits transfer of the invasion plasmid in the construction of new vaccine strains
S. flexneri 2a (CVD 1207) Δset1A Inactivates enterotoxin ShET1 (9, 10, 26)