FIG. 2.
Persistence and stability of serovar Typhi strains harboring pHUR3. (A) Intracellular survival of recombinant serovar Typhi strains in the human monocytic cell line U937. The plot shows the number of salmonellae recovered from cultures of PMA-activated U937 cells (5 × 105 per well) infected with strains carrying pHUR3 or with their plasmid-free parental controls (multiplicity of infection = 10:1). SY5915 and SY5917 CFU were enumerated in plain LB-aro agar (solid lines) or LB-aro agar containing ampicillin (dotted lines). Values represent the mean CFU/well of triplicate wells. Results shown are representative of three separate experiments in which the four bacterial strains were tested concurrently. (B) Persistence and stability of recombinant serovar Typhi strains in mice infected intranasally (108 CFU per mouse). Plot shows the number of recombinant salmonellae recovered from the lungs of mice infected with CVD908, SY5915, CVD908-htrA, or SY5917. Bacteria were enumerated in LB-aro agar (L; solid symbols) or LB-aro with ampicillin (Ap; open symbols). Data shown have been compiled from two separate experiments in which plasmid-free control and pHUR3-harboring strains were tested concurrently. Bars represent geometric means. ∗, P = 0.008 in Student's t test.