Table 2.

Invasiveness of wild-type serovar Typhi strain Ty2 and vaccine strains CVD 908-htrA and CVD 909 for Henle 407 cells in tissue culture

StrainRelevant phenotypeExptGeometric mean CFUa per well after Henle 407 cell lysis (SD)
0 h4 h
Ty2Wild type; regulated Vi expression16.86 × 104 (1.42) b5.03 × 105 (2.05) c
24.68 × 105 (1.02) d2.54 × 106 (1.66) e
CVD 908-htrA Vaccine strain; regulated Vi expression15.43 × 103 (1.04) f1.30 × 104 (1.41) g
29.03 × 103 (2.27) h3.00 × 104 (1.04) i
CVD 909Vaccine strain; constitutive Vi expression17.52 × 102 (1.08) j1.05 × 103 (1.39) k
28.72 × 102 (1.70) l1.08 × 103 (1.26) m
  • a Geometric mean of duplicate wells. Comparisons by Student's t test: b versus f, P = 0.06; f versus j, P = 0.005; d versus h, P = 0.092; h versus l, P = 0.095; c versus g, P = 0.049; g versus k, P = 0.017; e versus i, P = 0.048; and i versus m, P = 0.026. Overall probability using Fisher's test of combined probabilities: Ty2 versus CVD 908-htrA, P = 0.034 and P = 0.017 at 0 and 4 h, respectively; CVD 908-htrA versus CVD 909, P = 0.004 and P = 0.004 at 0 and 4 h, respectively.