Once past the physical barriers, pathogens must interact with host cells to establish infection. This interaction can be highly specific, often involving receptors on the host cell surface that bind to pathogen ligands. This binding can trigger several responses: - Endocytosis: Pathogens like Salmonella induce host cells to engulf them in vesicles. - Direct penetration: Some pathogens can directly penetrate the host cell membrane. - Intracellular survival: After entry, pathogens like Mycobacterium tuberculosis can survive within host cells by inhibiting phagosome-lysosome fusion.
