Pathogenic Mechanisms of Bacteria

Question 1

What are the two types of host defenses?

Answer 1

1) Body surfaces.

2) Defenses of tissues and blood.

Question 2

What is the first line of defense for the body?

Answer 2

Skin and mucosal surfaces.

Question 3

What are four defenses of the skin?

Answer 3

1) Dry, acidic pH conditions.
2) Low temperature (<37C).
3) Sloughing cells.
4) Resident micro flora.

Question 4

What is the function of the acidic conditions and low temperature of the skin?

Answer 4

To limit bacterial growth.

Question 5

What is the function of sloughing cells as a defense?

Answer 5

To remove bacteria from the skin’s surface.

Question 6

What is the function of the skin’s resident micro flora?

Answer 6

To compete for colonization.

Question 7

What does SALT stand for?

Answer 7

Skin associated lymphoid tissue.

Question 8

What cells secrete mucus?

Answer 8

Goblet cells.

Question 9

How do mucous membranes participate in host defense?

Answer 9

Mucus secreted by goblet cells acts as a lubricant. It acts as a physical barrier that traps bacteria before they reach the membrane itself.

Question 10

What does mucus secrete?

Answer 10

Secretory immunoglobulin A.

Question 11

What are three substances that mucus contains that either kill bacteria or inhibit their growth?

Answer 11

1) Lysozyme.
2) Lactoferrin.
3) Lacto peroxidase.

Question 12

What does lysozyme do?

Answer 12

It splits the muramic acid linkage in bacterial cells and degrades bacterial peptidoglycan.

Question 13

What type of bacteria is lysosyme extremely effective against?

Answer 13

Gram-positive bacteria.

Question 14

What does lactoferrin do?

Answer 14

Lactoferrin is a protein that binds iron with a high affinity. Iron is an essential nutrient for bacteria. Most bacteria are unable to compete with lactoferrin for iron. Thus lactoferrin reduces iron availability to bacteria.

Question 15

Where is lactoferrin found?

Answer 15

Lactoferrin is found in milk and many mucosal secretions, such as tears and saliva.

Question 16

What is lacto peroxidase?

Answer 16

It has been identified as an antimicrobial agent in milk, saliva, and tears. Lacto peroxidase is toxic to many bacteria.

Question 17

What does GALT stand for?

Answer 17

Gastrointestinal (gut) associated lymphoid tissue.

Question 18

What does MALT stand for?

Answer 18

Mucosa associated lymphoid tissue.

Question 19

What do GALT/MALT do?

Answer 19

They produce secretory antibody which prevents bacterial adherence to mucosal cells.

Question 20

What are five defensive substances of tissue and blood?

Answer 20

1) Transferrin.
2) PMNs.
3) Monocytes.
4) Macrophages.
5) Complement.

Question 21

What are four ways bacteria can survive inside PMN’s or macrophages?

Answer 21

1) Strategy to escape phagosome before it fuses with the lysosome.
2) Ability to prevent phagosome-lysosome fusion from occurring.
3) Preventing acidification of the vacuole or short-circuiting the process of fusion itself.
4) Reduce the effectiveness of the toxic compounds released into the phagolysosome after fusion occurs.

Question 22

What are pathogens?

Answer 22

Pathogens are disease-causing microorganisms.

Question 23

What is pathogenesis?

Answer 23

It is the physiological processes involved in the generation of clinical signs of disease or the means by which a pathogen causes illness.

Question 24

What is pathogenicity?

Answer 24

It is the capacity of a microbe to cause disease.

Question 25

What is virulence?

Answer 25

It is the ability of a microbe to cause disease efficiently (high virulence) or inefficiently (low virulence).

Question 26

What is a virulence factor?

Answer 26

It is a component of a pathogen that contributes to its disease-producing potential.

Question 27

What are Koch's postulates?

Answer 27

1) The organism must always be found in humans/animals with the infectious disease but not found in healthy ones. 2) The organism must be isolated from humans'animals with the infectious disease and grown in pure culture. 3) The organism isolated in pure culture must initiate disease when re-inoculated into susceptible animals. 4) The organism should be re-isolated from the experimentally infected animals.

Question 28

What is the pathogenic capacity of an organism determined by?

Answer 28

By its virulence factors.

Question 29

What are five methods by which pathogens cause disease?

Answer 29

1) Adhesion. 2) Colonization. 3) Invasion. 4) Immune response inhibitors. 5) Toxins.

Question 30

What bacterial species can penetrate the gut epithelial layer?

Answer 30

Salmonella typhimurium.

Question 31

What are the three routes by which Salmonella typhimurium can penetrate the gut epithelial layer?

Answer 31

1) Salmonellae enter and kill M cells and then infect macrophages and epithelial cells. 2) Salmonellae invade the luminal surface of epithelial cells. 3) Salmonellae enter dendrites of dendritic cells that are sampling the gut luminal contents.

Question 32

What are M cells?

Answer 32

They are epithelial cells found on the intestinal mucosa.

Question 33

What do M cells do?

Answer 33

They transport organisms and particles from the gut lumen to immune cells across the epithelial barrier, and thus are important in stimulating mucosal immunity.

Question 34

What is apoptosis?

Answer 34

It is a form of cell death in which a programmed sequence of events leads to the elimination of cells without releasing harmful substances into the surrounding area.

Question 35

What are the two major categories that virulence factors can be classified into?

Answer 35

1) Factors that promote bacterial colonization and invasion. | 2) Factors that cause damage to the host.

Question 36

What are five virulence factors that promote colonization and survival?

Answer 36

1) Fimbriae (pili). 2) Nonfimbrial adhesions. 3) Invasins. 4) Motility and chemotaxis. 5) IgA proteases.

Question 37

What is the best mechanism of adherence?

Answer 37

Attachment mediated by rod-shaped protein structures called pili or fimbriae.

Question 38

How are cell surface proteins on some bacteria help with adherence?

Answer 38

They mediate tighter binding of bacteria to the host cell.

Question 39

What are invasins?

Answer 39

Invasins are bacterial surface proteins that provoke phagocytic ingestion of the bacteria by host cells.

Question 40

How do capsules help bacteria survive?

Answer 40

They protect the bacteria from the host's inflammatory response (complement activation and phagocyte-mediated killing).

Question 41

What are siderophores?

Answer 41

Siderophores are low molecular weight compounds that chelate iron with very high affinity.

Question 42

Why is iron important?

Answer 42

It is essential for bacterial growth and its concentration in nature are generally quite low.