Intro to Infectious Diseases, Cell Structure and Classification, Virulence

Question 1

Virulence:

Answer 1

The ability of an organism to cause disease.

Question 2

Three routes of disease transmission:

Answer 2

1. Exogenous microbes transmitted from one human to another human.
2. Exogenous microbes transmitted from animals to human.
3. Endogenous agents which are part of the normal flora.

Question 3

Fomites:

Answer 3

Inanimate objects which harbor microorganisms.

Question 4

Beneficial effects of normal flora (4):

Answer 4

1. Production of essential nutrients (vit. K).
2. Occupation of habitat.
3. Elaboration of toxic products.
4. Stimulation of the host immune response.

Question 5

Koch’s Postulates(4):

Answer 5

1. Bacterium should be found in all people who have the disease in parts of the body affected.
2. Bacterium should be isolated and maintained in pure culture.
3. Pure culture inoculated into another should produce disease symptoms.
4. Same bacterium should be reisolated in pure culture.

Question 6

Limitations/caveats to Koch’s postulates(5):

Answer 6

1. Ignores the role of host.
2. Importance of being able to culture bacterium.
3. Variability in virulence of a single bacterial species.
4. Ethical problems with 4th postulate.
5. Polymicrobial infections.

Question 7

Two types of viral infections:

Answer 7

1. Lytic cycle

2. Persistent or latent infections.

Question 8

Viroids:

Answer 8

Consist of RNA genome without any protein components.

Question 9

Prions:

Answer 9

Infectious agents consisting only of protein.

Question 10

Pili:

Answer 10

Thin, rigid appendages composed of proteins called pilins.

Allow cells to adhere to host cell or other bacterial cell surfaces.

Question 11

Cytoplasmic inclusion bodies:

Answer 11

Sites where nutrient macromolecules are stored as large complexes.

Question 12

Bacterial plasma membrane functions (3):

Answer 12

1. Site of active transport.
2. Respiratory chain components.
3. Site of synthesis for phospholipids, peptidoglycan, LPS and capsular polysaccharides.

Question 13

Bacterial cell envelope =

Answer 13

Plasma membrane + cell wall + intervening material

Question 14

Gram positive cell envelope key features (3):

Answer 14

1. Thick, multilayered peptidoglycan overlying plasma membrane.
2. Teichoic acids, lipoteichoic acid.
3. Plasma membrane

Question 15

Peptidoglycan functions/activities (4):

Answer 15

1. Allows diffusion of small molecules to the plasma membrane.
2. Confers rigidity and shape.
3. Interferes with phagocytosis.
4. Adjuvant, pyrogen and somnagen

Question 16

Teichoic acids:

Answer 16

Water-soluble polymers of either ribitol phosphate or glycerol phosphate that are covalently linked to peptidoglycan.

Question 17

Lipoteichoic acids:

Answer 17

Teichoic acids which terminate in a fatty acid that serves to anchor the molecule in the plasma membrane.

Question 18

Gram negative envelope key features (4):

Answer 18

1. Unique outer membrane which contains LPS.
2. Thin peptidoglycan overlaying plasma membrane.
3. Periplasmic space.
4. Inner (plasma) membrane.

Question 19

Which portion of LPS is responsible for endotoxic activity?

Answer 19

Lipid A

Question 20

Results of LPS in the bloodstream:

Answer 20

Synthesis of IL-1, TNF and other cytokines; complement and coagulation cascades are activated.

Question 21

Braun lipoprotein:

Answer 21

Covalently anchors the outer membrane to peptidoglycan. (Inner leaflet of outer membrane.)

Question 22

Omp proteins:

Answer 22

Stabilize the outer membrane and act as specific receptors.

Question 23

Three types of exotoxins:

Answer 23

1. AB toxins.
2. Pore-formers (hemolysins).
3. Superantigens

Question 24

Pore former exotoxin:

Answer 24

Acts to lyse the cell by permitting rapid water entry in response to the osmotic gradient.

Question 25

Phospholipase:

Answer 25

Enzymatically removes the charged head of phospholipids. Destabilizes the cell membrane, resulting in cell lysis.

Question 26

Adhesins

Answer 26

Bacterial surface proteins which mediate intimate contact with the host cell.

Question 27

Bacteria obtain iron (3):

Answer 27

1. Siderophores/enterobactins chelate iron and bring inside cell. 2. Receptors for transferrin, lactoferrin, etc. 3. Kill host cells to liberate intracellular iron.