A Salmonella typhimurium rfaE mutant recovers invasiveness for human epithelial cells when complemented by wild type rfaE (controlling biosynthesis of ADP-L-glycero-D-manno-Heptose-containing lipopolysaccharide)

Invasion of host cells is essential for the pathogenicity of Salmonella. The author's group has recently reported the cloning of the rfaE gene of Salmonella typhimurium, previously implicated in biosynthesis of the lipopolysaccharide (LPS)-inner core [Jin et al. (2001); Kim (2002)]. The product of the rfaE gene is involved in ADP-L-glycero-D-manno-heptose biosynthesis. rfaE mutants synthesize heptose-deficient LPS (Re-LPS) consisting only of lipid A and 3-deoxy-D-manno-octulosonic acid (KDO). Mutants that make incomplete LPS are rough mutants and "deep-rough" mutants affected in the heptose region of the inner core have reduced growth rate and increased sensitivity to high temperature. Complementation of S. typhimurium rfaE mutant strain SL1102 (rfaE543) with rfaE demonstrated conclusively that this gene restored the smooth phenotype, and the LPS produced by the complemented strain was indistinguishable from that of wild type smooth strains. In vitro infection experiments showed that complementation with rfaE permitted invasion of human Chang epithelial cells, larynx epidermal carcinoma HEp-2 cells and intestinal epithelial Henle-407 cells. These data imply that the structure of the LPS that is synthesized is critical for Salmonella invasiveness.