Expression of host resistance to Salmonella typhi and Salmonella typhimurium: bacterial survival within macrophages of murine and human origin

Cell-association of various strains of Salmonella typhi and Salmonella typhimurium with different populations of macrophages was studied. Macrophages were infected, exposed to gentamicin, washed, and counts of viable bacteria protected from gentamicin killing were made. J774A.1 cells, a continuous macrophage-like cell line, were the most permissive, all strains tested achieving similar high recoveries. Virulent S. typhimurium 779C-SmS, but not avirulent S. typhimurium 779C-SmD, survived well in mouse peritoneal macrophages and human monocyte-derived macrophages. Virulent S. typhi Ty2 were killed by mouse peritoneal macrophages, but were able to survive within human monocyte-derived macrophages. Viable counts of clinical isolates of S. typhi within the human monocyte-derived phagocytes were lower as compared with those of S. typhi Ty2. Phagocytosis of opsonized and non-opsonized virulent S. typhi Ty2 and S. typhimurium 779C-SmS by mouse peritoneal macrophages failed to trigger their respiratory burst as assessed by the intracellular reduction of nitroblue tetrazolium dye (NBT). These experiments support the view that the intracellular survival of Salmonella is in part host dependent and specific in nature. They also suggest that virulence influences the survival and intracellular multiplication of Salmonella within macrophages, and that their ultimate fate within macrophages may not be related to oxygen-dependent mechanisms.