Chromosomal DNA, iron-transport systems, outer membrane proteins, and enterotoxin (heat labile) production in...

We examined a representative collection of Salmonella typhi strains from Chile, Peru, Mexico, India, and England for the presence of several properties. All strains had a conserved pattern of outer membrane proteins, as determined by sodium dodecyl sulfate-polyacrylamide gel electrophoresis. The electrophoresis profiles of chromosomal DNA digested with EcoRI and PstI restriction enzymes were similar for all the strains. A conserved pattern of hybridization was observed when digested chromosomal DNA was hybridized with DNA probes for the 36-kilodalton porin, enterobactin synthesis, and enterobactin receptor genes. All the strains produced enterobactin but not aerobactin in bioassays. None of the strains produced heat-labile toxin, as measured by an enzyme-linked immunosorbent assay. Colony and Southern hybridizations with DNA probes for aerobactin synthesis and its receptor and heat-labile toxin genes were negative. These results indicate that S. typhi strains from different origins have similar phenotypic and genetic properties and, as has been suggested, constitute a clone.