1-21 Intracellular Bacteria

Question 1

what is unusual about chlamydia replication cycle?

Answer 1

has two morphs: reticulate and elementary bodies

Question 2

Explain the difference between obligate and facultative intracellular pathogens and the relevance of these terms to laboratory diagnosis of infection.

Answer 2

Obligate intracellular pathogens need a host cell to multiply

facultative intracellular pathogens grow and multiply independently, but enter the host cell as part of their pathogenesis.

Obligate intracellular pathogens must be grown in tissue culture.

Question 3

List the three major pathways by which intracellular pathogens survive endocytosis to establish infection.

Answer 3

Upon entering the host cell, intracellular pathogens can do the following:

Escape the endosome (break out before fusion with a lysosome)

Subvert the endosome (prevent lysosome fusion)

Survive lysosome fusion (live in the environment of the endolysosome)

Question 4

5 major recurring themes in intracellular pathogensis

Answer 4

1. use of infected macrophages for transport
2. Host cell takeover by type III secretion system
3. actin based motility and cell-cell spread
4. evasion of humoral immunity
5. need for antibiotics to penetrate human cell membrane

Question 5

example of use of infected macrophages for transport

Answer 5

salmonella is engulfed by macrophage, uses it as trojan horse to get around the body

Question 6

example of host cell takeover by type 3 secretions systems

Answer 6

shigella

either enhances phagocytosis in target cell type

or

alters the phagosome so that the lysosome fails to fuse

Question 7

actin-based motility and cell-cell spread

Answer 7

listeria - polymerizes actin (using ActA virulence factor) and uses it for motility and to break out of cell to cell-cell penetrate adjacent cell

Question 8

evasion of humoral immunity

Answer 8

pathogen uses variety of mechanisms to avoid being neutralized by host humoral immunity

enteric bacteria using M cells as gateways to exterior surface of intestine,

Question 9

the need for antibiotics to penetrate human cell membrane

Answer 9

in order to reach the intracelluar pathogens within the cells, antibiotics must be able to get to them

tetracyclines

Question 10

antibiotics for intracellular?

Answer 10

tetracyclines

azith or chloramphenicol if pregnant

Question 11

advantage of chlamydia’s different forms?

Answer 11

EB - tiny, rugged, great for hopping host to host but too compact to efficiently reproduce

RB’s - large and complex, great for reproducing but too delicate to survive outside host cell