FIG. 3.

Scanning electron micrographs of the S. typhimurium strains carrying mutations in invG (strain 83; A to E) or in sspC (strain EE638; F). When adhering to cell-free culture supports (A), S. typhimurium 83 lacked any of the short filamentous appendages observed on a proportion of cells of wild-type and invA mutant S. typhimurium strains (see, e.g., Fig. 1F and 2D), although longer filamentous appendages were occasionally observed. When adhering to MDCK cells (B) or Caco-2 cells (C), a variable proportion of S. typhimurium 83 cells formed numerous short filamentous appendages indistinguishable from those seen on wild-type bacteria. Similar surface features were also present on some S. typhimurium 83 cells adhering to M cells (D) and enterocytes (E) after infection of murine Peyer’s patches in ligated intestinal loops. S. typhimurium EE638 also produced short filamentous appendages when adhering to MDCK or Caco-2 cells (F); these appendages generally more closely resembled those observed on S. typhimurium invA mutant SB111. Bars, 2 μm.