Chapter 15: Microbial Mechanisms of Pathogenicity

Question 1

Pathogenicity:

Answer 1

The ability to cause disease.

Question 2

Virulence:

Answer 2

The degree of pathogenicity. The ability of pathogen to cause disease, and how dangerous/deadly is.

Question 3

Routes of microbial entry:

Answer 3

1. Mucous membranes
2. Skin
3. Parenteral route
4. Preferred portal of entry

Question 4

1. Mucous membrane:

Answer 4

a) Respiratory tract: nose/motuh; common cold, influenza.
b) Gastrointestinal tract: food/water, dirty fingers; cholera.
c) Genitourinary tract: sexually contracted; HIV.
d) Conjuctiva: eyelids/white of eyeballs; conjuntivitis.

Question 5

2. Skin:

Answer 5

Gain access through hair follicles and sweat glands.

Question 6

3. Parenteral route:

Answer 6

Deposited directly into tissues when barriers are penetrated. Ex: punctures, injections, bites, cuts = HIV, tetanus, gangrene.

Question 7

4. Preferred portal of entry:

Answer 7

• Cause infections through their specific portal of entry.

This is important because bacteria cannot survive in some regions of the body but can flourish in other.
Ex: Salmonella typhi, skin is not a good portal, prefers to be swallowed.

Question 8

What type of action exposes microbes to each specific mucous membrane?

Question 9

ID50

Answer 9

Infectious Dose for 50% of sample population.

Measures the virulence of a microbe.

Question 10

LD50

Answer 10

Lethal Dose for 50% of sample population.

Measures potency of a toxin.

Question 11

How do capsules help bacteria evade the immune system?

Answer 11

Prevents phagocytic cell from adhering to the bacterium.

• Capsule= virulent (makes it ‘slippery’ to immune system)
• No capsule= avirulent (still infected but won’t cause disease)

Question 12

Enzymes that facilitate microbial colonization of the human body:

Answer 12

Enzymes are often secreted by the invading organism (bacteria).

a) Coagulases

b) Kinases

c) Hyaluronidase

d) Collagenase

e) IgA protease

Question 13

a) Coagulases:

Answer 13

Clots blood and forms a barrier to protect from phagocytosis (immune cells) and other body defenses

Question 14

b) Kinases:

Answer 14

Breaks down blood clots formed, to get released in bloodstream and infect more.

Question 15

c) Hyaluronidase:

Answer 15

Holds together connective tissue; (Contributes to pathogenicity by helping organism spread. (gangrene)

Question 16

d) Collagenase:

Answer 16

Helps break down collagen from tissue; facilitates spread of gangrene.

Question 17

e) IgA protease:

Answer 17

Destroys IgA antibodies (mucus membranes)
(Contributes to pathogenicity by inhibiting immune response)

Question 18

Ways bacteria can damage host’s cells:

Answer 18

1. Using hosts nutrients
2. Causing direct damage in the immediate vicinity of the invasion.
3. Producing toxins transported by blood and lymph, that damage sites far removed.

Question 19

Hemolysin:

Answer 19

Membrane disrupting toxins that lyses open red blood cells (erythrocytes), by forming protein channels.

Kills RBC to better outcompete for iron nutrients; helps invade host and lyse of RBC gives iron to pathogens.
(Contributes to pathogenicity by supplying nutrients for growth)

Question 20

Siderophore:

Answer 20

Proteins secreted by pathogens that bind iron more tightly that host cells (contributes to pathogenicity by steal/taking iron from us)

Question 21

Endotoxin:

Answer 21

Toxins that are part of the bacterial cell ( not a product )

Lipid A is the ONLY endotoxin. They are only found in (the outer wall) Gram-Negative bacteria.

Question 22

Exotoxin:

Answer 22

Toxins secreted from the bacterial cell (product release outside).

Can be found in Gram positive(mostly) and negative.

Question 23

Types of Exotoxins:

Answer 23

A) Type l: Superantigens.
B) Type ll: Membrane-disrupting toxins.
C) Type lll: A-B toxins

Question 24

A) Type l: Superantigens

Answer 24

cause an immune response due to release of cytokines from host cells.
Symptoms of fever, nausea, vomiting, diarrhea and death.

Question 25

B) Type ll: Membrane-Disrupting toxins

Answer 25

Lyse host cells by disrupting plasma membranes.
-Leukocidins, Hemolysins, Streptolysins.

Question 26

C) Type lll: A-B Toxins

Answer 26

(Most common and potent)
Contain an enzyme component (A) and a binding component (B).

Question 27

Fungal toxins:

Answer 27

-Ergot
-Aflatoxin
-Mycotoxins
-Phalloidin and amanitin

Question 28

What is LAL and why is it important to the pharmaceutical industry:

Answer 28

Limulus amebocyte lysate (LAL) assay

Is found in horseshoe crab blood. It is used to detect (test) the presence and concentration of bacterial endotoxins in drugs and biological products. Coagulates any gram- bacteria or lipid A.

Question 29

How are capsules and cell wall components related to pathogenicity?

Answer 29

Encapsulated bacteria can resist phagocytosis and keep growing.
Ex: Mycobacterium: mycolic acid resists digestion by phagocytes.

Question 30

Describe how leukocidins might contribute to pathogenicity

Answer 30

By destroying neutrophils and macrophages that are active in phagocytosis; this decreases host resistance to infection.