Unusual intracellular trafficking of Salmonella typhimurium in human melanoma cells

Salmonella spp. are enterobacteria capable of invading and replicating in both professional and non‐professional phagocytes. Here, we investigate the fate of S. typhimurium in human melanoma MelJuSo cells. The bacterium entered MelJuSo cells by a trigger mechanism and resided within a unique organelle, the Salmonella‐containing vacuole (SCV). The SCV acquired early endosomal markers transiently and then underwent a series of membrane modifications. In HeLa cells, vacuole maturation is characterized by the simultaneous acquisition of the lysosomal membrane glycoproteins (Lgps) Lamp1, CD63 and vacuolar (v)‐ATPase; in MelJuSo cells, however, acquisition of CD63 and v‐ATPase preceded that of Lamp1. A very striking event in MelJuSo cells was the arrest of bacterial septation starting from 8 h after infection. Bacteria nevertheless continued to elongate, remained morphologically intact and viable and were eventually exocytosed. This original feature was observed in several skin‐related cells including melanocytes, suggesting that it may provide the basis for an efficient host defence mechanism against Salmonella infection.