Cell-free, unconcentrated sonic extracts of several serotypes of Salmonella caused extensive detachment of intact Vero cells. Undiluted sonic extracts of these strains exhibited cell detachment in the range 20 - 50%. Upon dilution, the extract preparations caused a linear, dose-related cytotoxic effect on Vero cell monolayers. The heat-lability (100°C for 30 min) of much of the cytotoxic activity in the extract ruled out the possible involvement of endotoxin in this toxic effect for eukaryotic cells and suggested that this toxic factor is probably a protein. It was demonstrated that these sonic extracts also inhibited the incorporation of 3H-leucine by Vero cells and that the inhibitory events occurred 1 - 2 hr after exposure. When subjected to heating at 100°C for 30 min, the ability of Salmonella extracts to inhibit protein synthesis of Vero cells was significantly but only partially destroyed. Because the Salmonella extract-treated Vero cells did not release 3H-uridine until 24 - 48 hr after addition of sonic extracts, cell lysis was considered to be a secondary event resulting from the early shutdown of protein syntheis, rather than a direct effect of the toxic factor on membrane integrity. Further studies are needed to determine if these two biological activities of Salmonella sonic extracts are due to a single toxic molecule or result from two distinct toxin molecules.
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