Multiplication of Shigella flexneri within HeLa cells: lysis of the phagocytic vacuole and plasmid-mediated contact hemolysis

TLDR

Virulent strains of *Shigella flexneri* invade HeLa cells efficiently, a process encoded by a 140‑megadalton plasmid that induces bacterial phagocytosis. The authors aim to show that the virulence plasmid and its hemolysin drive rapid intracellular growth and invasion of *Shigella* spp. They used the full virulence plasmid pWR100 and its 32‑megadalton subclone pHS4108 to assess plasmid‑mediated intracellular growth in HeLa cells. Intracellular replication correlated with plasmid‑mediated phagocytic vacuole lysis and hemolytic activity, but not with Shiga toxin induction. The experiments were performed in mammalian cells.

Abstract

Virulent strains of Shigella flexneri invade HeLa cells with high efficiency. This crucial step in the pathogenic process is encoded by a 140-megadalton plasmid which induces phagocytosis of the bacteria by host cells. In this report we used pWR100, the virulence plasmid of S. flexneri serotype 5, and pHS4108, a 32-megadalton subclone of pWR100, to demonstrate that the plasmid is also responsible for rapid intracellular growth of the bacteria. The ability to replicate intracellularly was not correlated with induction of Shiga toxin. However, plasmid-mediated intracellular multiplication was strongly correlated with the ability of the bacteria to rapidly and efficiently lyse the phagocytic vacuole and replicate freely in the cytoplasm. Temperature-regulated plasmid-mediated contact hemolytic activity strongly correlated with both phagosomal membrane lysis and efficient intracellular multiplication. We propose this virulence plasmid-associated hemolysin to be an important factor in the invasion and proliferation of Shigella spp. in mammalian cells.