[Two multidrug-resistant Salmonella infantis isolates behave like hypo-invasive strains but have high intracellular...

In this work, plasmid-encoded virulence factors in two Salmonella Infantis isolates carrying multiresistance plasmids were investigated. In addition, their invasion and proliferative ability in non-phagocytic cells was studied. None of them showed the typical determinants of virulence plasmids (spy operon). The invasion assays of S. Infantis isolates on eukaryotic cells showed a decreased ability to invade but they remained and proliferated in the cytoplasm regardless of having used a permissive (HeLa) or non-permissive (NRK) cell line. Finally, there was no microscopic evidence suggesting a bactericidal effect of these eukaryotic cell lines on the isolates tested.