Intracellular replication of Salmonella within epithelial cells is associated with filamentous structures containing lysosomal membrane glycoproteins.

We have examined the targeting of S. typhimurium-containing vacuoles to lysosomes after invasion of cultured HeLa epithelial cells. Our results show that intracellular bacteria colocalize with vacuoles containing lysosomal membrane glycoproteins (LGPs). Both human LGPs, hlamp-1 and hlamp-2, are present in S. typhimurium-containing vacuoles from approximately 2 h postinfection. At later times (4-6 h), long and stable filamentous structures with lysosomal markers appear connected to bacteria-containing vacuoles in infected cells. Viable intracellular bacteria are required for the formation of these structures, which are not detected in uninfected cells or in HeLa epithelial cells infected with another invasive bacteria, Yersinia enterocolitica. Kinetics analysis showed a strict correlation between the appearance of these LGP-rich filaments and the initiation of intracellular bacterial replication. Moreover, these structures are absent in epithelial cells infected with certain S. typhimurium intracellular replication-defective mutants. Additional data confirmed that an intact microtubule network and intravacuolar acidic pH are required to induce the formation of LGP-containing filamentous structures and that these structures are morphologically and functionally different from previously described tubular lysosomes.