Lecture 21 Infection and Pathogenesis

Question 1

What factors influence the outcome of the relationship between a host and a pathogen

Answer 1

-age, immune, and health status
-number of pathogens exposed to
-virulence of pathogen (invasiveness, infectivity, pathogenic potential, toxigenicity)

Question 2

What are the stages in the clinical course of infectious disease?

Answer 2

1. incubation period (prior to symptoms)
2. prodrome (non-specific symptoms, fatigue)
3. illness (symptoms)
4. convalescence (recovery)

Question 3

What are the essential factors for the development of an infectious disease?

Answer 3

1. resevoir
2. transport/transmission to the host
3. attachment, entry, and colonization of the host
4. evasion of host defence mech
5. multiply and complete the lifecycle
6. mechanically/chemically damage the host
7. exit the host and return to the resevoir or cause new infections

Question 4

What are the different ways of transmission?

Answer 4

Direct
- kissing, sex
-airborne droplets (talking)
-vector (insects)
-vertical contract (baby)

Indirect
-contact
-food, biological properties
-airborne

Question 5

Name of disease transmitted from an animal to human?

Answer 5

zoonosis/zoonotic disease

Question 6

What are the key factors involved in the colonization of a pathogen in host?

Answer 6

-portal of entry
-attachment to host cell
-invasion of host cell (active vs passive)
-growth

Question 7

How do pathogens survive and evade host defenses?

Answer 7

outcompete host microbiotia through direct and indirect mechanisms (toxins),
constantly modify surface proteins

survival and evasion of immune system.

evade detection Virulence factor

Question 8

What are pathogenicity islands?

Answer 8

They encode virulence factors in pathogenic species.

Can convert non-pathogenic to pathogenic

can be transferred by horizontal gene transfer

Question 9

What is the difference between endotoxin and exotoxin?

Answer 9

Exotoxins (g+ and g-)
multiple mech (a/b, pore forming toxins, superanttigens)
heat-labile proteins

Endotoxins (g- cell wall)
Lipid A in LPS of Gram negative pathogens
Overexpression of pro-inflammatory cytokines leading to apoptosis

Question 10

What makes a good pathogen?

Answer 10

ability to…
1. evasiveness (ability to access host)
2. toxicity (the strength/ability to damage)
3. infectivity (ability to grow fast and spread)

Question 11

What are some virulence factors of Staphylococcus aureus?

Answer 11

-coagulase production (creates clots)
-super antigen production
(protein A on membrane interferes with antibody binding)

damage host (TSS strong immune response)

Question 12

What are the characteristics of E.coli O157: H7?

Answer 12

contain both
Enterohemorrhagic E. coli (EHEC)
Shiga-toxin-producing E. coli (STEC)

type 1 fimbriae attachment
endotoxin prod
(indirect effect cause cytokine storm)
A or B-hemolysin production (fully lysed red blood cells)
Exotoxin-producing (shiga) causing damage to blood cells

Question 13

How does the gut microbiome contribute to preventing infections?

Answer 13

colonization resistance
competitive exclusion
bacterial interference
direct (bacteriocins) and indirect (innate immune) mechanisms

Question 14

What do type 1 toxins do?

Answer 14

Disrupt host cells indirectly, without entering them, create an overreaction and strong immune response resulting in cytokine storms.

AKA; superantigens, excessive immune response (toxic shock syndrome)

Question 15

What do type 2 toxins do?

Answer 15

Directly invade host cells, causing damage to membranes (hemolysins and proteases)

as seen in botulism toxin, lead to host cell invasion and membrane damage

Question 16

What do type 3 toxins do?

Answer 16

Enter host cells to cause damage using a receptor, with active (A) and binding (B) components.

Utilizes host cell machinery for entry, with B component facilitating binding and A component causing cellular damage.

example: Cholera and Shiga toxins, for instance, bind to host cell receptors, enter via endosomes, and release active components causing damage.