Bacterial strains, plasmids, and growth conditions.

The bacterial strains and plasmids utilized herein are described in Table 1. E. coli strains were grown at 37°C in Luria-Bertani (LB) broth or on LB agar from Difco. Shigella strains were grown in tryptic soy broth (TSB) or tryptic soy agar (TSA) from Difco. Salmonella strain Ty21a or derivatives were grown in TSB or on TSA. For growth comparisons, Ty21a and derivative strains were grown at 37°C in TSB with 0.01% galactose supplementation or a casein-yeast extract (CY) medium with 0.01% galactose supplementation (CY medium is currently used to manufacture Vivotif; Kopecko et al. [28]). Plasmid-containing strains were selected in growth medium containing ampicillin (Amp; 100 μg/ml), spectinomycin (Spc; 100 μg/ml), chloramphenicol (Cm; 35 μg/ml), or kanamycin (Kan; 30 μg/ml). All constructed plasmids were sequenced, and the sequences were assembled and analyzed using the Vector NTI suite 9.0 software (Invitrogen).