Transmission electron micrographs and motility assays of wild-type Salmonella and mutant Salmonella strains. A, wild-type Salmonella; B, spiC mutant strain; C, spiC mutant strain carrying pEG9127; D, spiR mutant strain; and E, ssaV mutant strain. The spiC mutant had no flagella or only a single flagellum, and the defective formation of flagella filaments in the spiC mutant could be restored to the wild-type phenotype by introducing pEG9127 into the spiC mutant. Bars represent 2 μm. (F) Motility assay of the wild-type Salmonella and mutant Salmonella strains. 1, wild-type Salmonella; 2, spiC mutant strain; 3, spiC mutant strain carrying pEG9127; 4, spiR mutant strain; 5, ssaV mutant strain; and 6, flhD mutant strain. Bacteria were inoculated on a semisolid LB plate containing 0.25% agar and incubated for 5 h at 37°C. The wild-type strain, the complemented spiC mutant, and the ssaV mutant made large swarming rings, but the spiC and spiR mutants had weak swarming abilities.