Rapid and complete fusion of macrophage lysosomes with phagosomes containing Salmonella typhimurium

Abstract

The virulence of Salmonella typhimurium for mice results, in part, from its ability to survive after phagocytosis by macrophages. Although it is generally agreed that intracellular bacteria persist in membrane-bound phagosomes, there remains some question as to whether these phagosomes fuse with macrophage lysosomes. This report describes the maturation of phagosomes containing S. typhimurium inside mouse bone marrowderived macrophages. Macrophages were infected briefly and incubated for various intervals; then they were examined by fluorescence microscopy for colocalization of bacteria with lysosomal markers. These markers included LAMP-1, cathepsin L, and fluorescent proteins or dextrans preloaded into lysosomes by endocytosis. By all measures, phagosomes containing S. typhimurium merged completely with the lysosomal compartment within 20 min of phagocytosis. The rate of phagosome-lysosome fusion was similar to the rate for phagocytosed latex beads. Phagolysosomes remained accessible to fluid-phase probes and contained lysosomal markers for many hours. Moreover, a large percentage of the wild-type bacteria that were viable 20 min after infection survived longer incubations inside macrophages, indicating that the survivors were not a minor subpopulation that avoided phagosome-lysosome fusion. Therefore, we conclude that S. typhimurium survives within the lysosomal compartments of macrophages.

Salmonella infection of bone marrow-derived macrophages and dendritic cells: influence on antigen presentation and initiating an immune response

“…S. typhimurium is a Gram-negative bacterium that survives and replicates inside infected Mx [21], remaining con¢ned inside vacuoles in the infected cells [22]. S. typhimurium has evolved a series of strategies to survive inside the harsh milieu of phagolysosomal compartments of phagocytic cells including delaying acidi¢cation of phagosomes containing bacteria, inducing tolerance to acid stress, and being resistant to a family of antimicrobial peptides called defensins [23].…”

Live attenuated Salmonella: a paradigm of mucosal vaccines

“…Rather, S. typhimurium controls the molecular composition of the vacuole. Salmonella-specific vacuoles, which contain some lysosomal markers, including LAMPl, lysosomal acid phosphatase, hut uot cathepsin L nor the mannose-6 phosphate receptor, remain accessible to fluid phase markers(149,150). Nevertheless, heat-killed bacteria reach the degradative compartment positive for all lysosomal markers mentioned above.…”

Targeting host lipid flows: Exploring new antiviral and antibiotic strategies

“…After entering cells, A. phagocytophilum, Brucella, Mycobacterium, Salmonella, Chlamydia, and Coxiella burnetii establish their replicative inclusions in membrane-bound compartments derived from phagosomes or organelles of the endocytic pathway (Alpuche-Aranda, Berthiaume, Mock, Swanson, & Miller, 1995;Heinzen, Scidmore, Rockey, & Hackstadt, 1996;Niu, Yamaguchi, & Rikihisa, 2008;Oh et al, 1996). Although these bacteria lack the genes for cholesterol biosynthesis, cholesterol content increases in infected cells.…”