Unusual intracellular trafficking of Salmonella typhimurium in human melanoma cells

Salmonella spp. are enterobacteria capable of invading and replicating in b oth professional and non-professional phagocytes. Here, we investigate the fate of S. typhimurium in human melanoma MelJuSo cells. The bacterium enter ed MelJuSo cells by a trigger mechanism and resided within a unique organel le, the Salmonella-containing vacuole (SCV). The SCV acquired early endosom al markers transiently and then underwent a series of membrane modification s. In HeLa cells, vacuole maturation is characterized by the simultaneous a cquisition of the lysosomal membrane glycoproteins (Lgps) Lamp1, CD63 and v acuolar (v)-ATPase; in MelJuSo cells, however, acquisition of CD63 and v-AT Pase 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 via ble and were eventually exocytosed. This original feature was observed in s everal skin-related cells including melanocytes, suggesting that it may pro vide the basis for an efficient host defence mechanism against Salmonella i nfection.