9-4 IMM Microbial Pathogenesis and Mechanism of Virulence

Question 1

Pathogen definition

Answer 1

organism that can cause disease

Question 2

Pathogenesis definition

Answer 2

process resulting in disease

Question 3

Virulence definition

Answer 3

degree of damage or disease resulting from infection

Question 4

Infectivity definition

Answer 4

likelihood of causing infection/disease with exposure to a particular dose

Question 5

How infectious is E. Col?

Answer 5

ID50 ranges from 10^1 to 10^3 colony forming units for different strains

Question 6

Rhinovirus

Answer 6

• common cold

- high infectivity, low virulence

Question 7

Influenza virus

Answer 7

• moderate infectivity, greater virulence, host dependent

Question 8

Ebola virus

Answer 8

• causes hemorrhagic fever

- high infectivity, high virulence

Question 9

Fomite disease transfer

Answer 9

From inanimate object

Question 10

Microbial virulence factors (3)

Answer 10

1) structures involved in attachment, adherence and invasion
2) toxins involved in cell or tissue damage
3) processes involved in immune avoidance

Question 11

Bacterial pili (fimbriae)

Answer 11

• filamentous structures extending from the bacterial surface
• important for adherence to host cell
• can be homo or heterodimers

Question 12

Type IV pili

Answer 12

• can extend, bind, retract

- promotes surface motility, microcolony and biofilm formation, adherence to host cell and immune evasion

Question 13

Pili vs flagella

Answer 13

Pili: shorter, thinner, more numerous and usually for attachment
Flagella: longer, thicker, fewer and for locomotion

Question 14

Gram - bacteria use type __ (3 types) to inject substrates into other cells

Answer 14

Type III, IV and V

Question 15

Viral attachment for naked viruses

Answer 15

• done by capsid proteins on naked virus
• virus enters via endocytosis
• example: adenovirus

Question 16

Viral attachment for enveloped viruses

Answer 16

• done by glycoprotein spikes on enveloped virus
• virus enters via membrane fusion or endocytosis
• example: HIV

Question 17

HIV attachment

Answer 17

• 2 part glycoprotein spike (GP120 and GP41)
• GP120 binds to CD4 on human T cell
• GP41 can then bind and initiates viral envelope fusion with host cell

Question 18

Cholera toxin

Answer 18

• A subunit activates adenylate cyclase, increases cAMP, promotes secretion of electrolytes and fluid by intestinal cells = profuse watery diarrhea

Question 19

Anthrax toxin

Answer 19

• A subunits Edema Factor (EF) and Lethal Factor (LF)
• EF activates adenylate cyclase
• LF cleaves cellular kinase leading to altered signaling and cell death

Question 20

Diphtheria

Answer 20

• A subunit inhibits protein synthesis

Question 21

Tetanus

Answer 21

• A subunit inhibits neurotransmitter release from inhibitory neurons in CNS resulting in spastic paralysis

Question 22

Pertussis (whooping cough)

Answer 22

• A subunit inhibits adenylate cyclase, increases cAMP in neutrophils and macrophages, decreases phagocytosis

Question 23

Example of pore-forming toxin

Answer 23

S. aureus

Question 24

Superantigen definition

Answer 24

bypasses antigen specificity of receptor

Question 25

Polysaccharide capsules

Answer 25

• extracellular, attached to gram - or + bacterial surface
• defines different serotypes of pathogen
• avoids phagocytosis and immune recognition
• common feature of pathogens that can disseminate via bloodstream to CNS

Question 26

Antigenic variation

Answer 26

• during infection, pathogens express different versions of key antigens so antibodies made against one version don’t recognize later versions
• Examples: trypanosoma brucei protozoan (sleeping sickness)

Question 27

Ways of avoiding immune surveillance

Answer 27

• biofilms
• mycobacterium tb induces formulation of “granulomas,” slowly replicating bacteria inside aggregates of dead cells
• Herpes virus travels from periphery to dorsal root ganglia and lay dormant in sensory neurons
• treponema pallidum produces very few surface proteins - teflon pathogen of syphillis

Question 28

Supressing immune system

Answer 28

• HIV destroys CD4+ cells
• M. tuberculosis prevents fusion of phagosomes and lysosomes in macrophages
• staphylococcal protein A binds IgG by the Fc region