Characterization of a Salmonella choleraesuis mutant that cannot multiply within epithelial cells

A mutant of Salmonella choleraesuis was identified that could invade (enter) and penetrate through polarized monolayers of Caco-2 and MDCK epithelial cells at normal levels but was defective for intracellular multiplication within these cells. It was also able to survive inside cultured J774 macrophage cells. These bacteria remained inside membrane-bound vacuoles, which coalesced at later times in the perinuclear region of the epithelial cell. This mutant exhibited slightly slower growth rates in rich or minimal media than the parental strain but was normal for iron usage, phosphate usage, and anaerobic growth and was a prototroph. The mutant was completely avirulent when administered orally or intravenously to susceptible mice. These results suggest that the ability to multiply within eukaryotic cells may contribute to S. choleraesuis virulence.