Host defense against Bacterial Infections

Question 1

Two impt host defenses

Answer 1

Intact epitheliun: ciliary mucosa (bronchi, middle ear, upper UG tract), macrophages (alveoli), acidicty, normal flora (nasopharynx, vagina)
Phagocytic cells: neutrophils, monocytes/macrophages/DC

Question 2

Vaccines

Answer 2

Another form of defense

• Killed-inactivated
• Subunit-acellular
• Live attenuated-
• Toxoid-chemically inactivated or mutated toxin which retain antigenicity

Question 3

Bugs that cause infx without invasion

Answer 3

colonize and secrete toxin on mucosal surface
toxin could act locally w/ or w/o tissue damange
or could migrate away from local tissue –> systemic effects

Question 4

Diptheria

Answer 4

Restricted to nasaopharynx but will release toxin that disseminate to organs to cause systemic manifestation-airway obstruction & damage to heart muscle. bug on surface but toxin go far

Question 5

Tissue Invasion

Answer 5

Few bugs penetrate skin. Quite a few invade mucosal epithelium by inducing epithelium cells to become phagocytic cells-direct manipulation of cytoskeleton to promote bug uptake (salmonella does this)

Question 6

Once bug gets past epithelial surface, how do they avoid phagocytic cells

Answer 6

**Avoid phagocytosis
-Hide from phagocyte
Intracellular replication in non-phagocytic cells
-Destroy phagocyte or inhibit phagocytic activity
Membrane damaging toxins
-Antiphagocyic surface properties
Inhibition of complement fixation

**Survive phagocytosis
-Escape from phagocytic vacuole (phagosome)
-Inhibit phagosome-lysosome fusion
-Survive antibacterial activities of phagolysosome
Reactive oxygen and nitrogen, antibacterial peptides