Pathogenesis: Invasion

Question 1

Why bacteria invade host cells?

Answer 1

• Access to ready supply of nutrients
• Protection from host defenses

Question 2

Majority of bacterial pathogens are BLANK cellular pathogens

Answer 2

extra

Question 3

Obligate intracellular bacteria

Answer 3

• Replicate only within host cells
• Rickettsia, Chlamydia

Question 4

Facultative intracellular bacteria

Answer 4

• Can replicate intra- and extracellularly
• Salmonella, Listeria, Mycobacterium

Question 5

Invasion of phagocytic cells requires pathogens to do what?

Answer 5

possess the ability to counteract the killing ability of phagocytes

Question 6

Invasion of non-phagocytic cells (eg. epithelial cells) requires?

Answer 6

bacteria produce molecules called Invasins to alter host cell cytoskeleton to promote the uptake of a bacterium

Question 7

invasins

Answer 7

Bacterial proteins that provoke engulfment of the bacterium by non-phagocytic host cells

Question 8

Type III protein secretion system

Answer 8

• serves to inject signaling proteins (invasins or effector proteins) from the pathogen directly into the host cell
• Injected effectors promote the cytoskeleton rearrangement in host cell: polymerization and de-polymerization of actin
• Promotes the engulfment and uptake of a bacterium by a (non- phagocytic) host cell

Thus, the pathogen is in effect forcing phagocytosis by eliciting formation of pseudopod-like structures by rearranging host cell cytoskeleton.

Question 9

Once inside a phagocytic cell, an intracellular pathogen can reside in one of the three general intracellular niches

Answer 9

• inside a phagosome vacuole which has not yet fused with a lysosome
• within a phagolysosome that has acidic environment with hydrolytic enzymes
• and in the host cell cytosol.

Question 10

Which bacterial pathogens have evolved many mechanisms to survive inside a phagosome vacuole which has not yet fused with a lysosome?

Answer 10

• Legionella pneumophila
• Salmonella Typhimurium
• Mycobacterium tuberculosis

Question 11

Legionella pneumophila

Answer 11

when taken up in a phagosome, prevent acidification and fusion with a lysosome. The vacuole becomes surrounded by endoplasmic reticulum-derived membranes. The bacteria replicate in the vacuole, escape the vacuole and lyse the phagocytic cell.

Question 12

Salmonella Typhimurium

Answer 12

when taken up by a macrophage, prevent a phagosome fusion with lysosome. The bacteria replicate in the specialized Salmonella-containing vacuole.

Question 13

Mycobacterium tuberculosis

Answer 13

is taken up into a phagosome. The bacterium prevents phagolysosome fusion by recruiting host proteins to the phagosome, while blocking recruitment of lysosomal hydrolases, so no acidification occurs. The bacteria replicate in the resulting vacuole.

Question 14

How have bacterial pathogens have evolved many mechanisms to survive inside harsh conditions of a phagolysosome