Microcheck 196

Skin is the most difficult barrier for a microbe to penetrate. Some pathogens induce mucosal epithelial cells to engulf the bacterium. Some pathogens exploit antigen-sampling processes, including transcytosis by M cells and phagocytosis.

■ How do Shigella species enter intestinal epithelial cells?

■ Why does Mycobacterium tuberculosis facilitate its own uptake by macrophages?

■ Why would some pathogens behave differently in a non-human host?

Bacteria move from cell to cell propelled by actin filaments.

(c) Pathogen (bacteria) released from macrophages enters host cells by endocytosis.

Tissue inside Mucous Membrane

Figure 19.6 Antigen-Sampling Processes Provide a Mechanism for Invasion Shigella species use M cells to traverse the epithelial barrier. Once on the other side, macrophages ingest them, but the bacteria are able to escape and then infect other cells.

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