Pathogenic mechanisms

Question 1

2 main host defenses (groups)

Answer 1

• body surfaces

- defenses of tissues and blood

Question 2

skin defenses (3)

Answer 2

• dry, acidic pH, and low temp
• sloughing cells
• resident microflora

Question 3

what does mucus contain to help with immunity (4)

Answer 3

• secretory immunoglobulin A
• lysozyme
• lactoferrin
• lactoperoxidase

Question 4

purpose of GALT/MALT

Answer 4

produce secretory antibodies –> prevents bacterial adherence to mucosal cells

Question 5

ways bacteria avoid killing by neutrophils (3)

Answer 5

• resist ingesion
• kill neutrophil
• grow inside phagocyte

Question 6

define: pathogens

Answer 6

disease causing microorganisms

Question 7

define: pathogenesis

Answer 7

the physiological process involved in the generation of clinical signs of disease (means by which a pathogen causes illness)

Question 8

define: pathogenicity

Answer 8

the capacity of a microbe to cause disease

Question 9

define: virulence

Answer 9

ability of a microbe to cause disease efficiently (also refers to degree of pathogenicity) –> case fatality rates, ability to invade host tissues

Question 10

define: virulence factor

Answer 10

component of a pathogen that contributes to its disease-producing potential (toxins, etc)

Question 11

koch’s postulates

Answer 11

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

Question 12

what is the pathogenic capacity of an organism determined by

Answer 12

its virulence factors

Question 13

methods by which pathogens cause disease (5)

Answer 13

• adhesion
• colonization
• invasion
• immune response inhibitors
• toxins

Question 14

functions of proteins produced by bacteria

Answer 14

• colonization of parts of the body
• disruption of cell membranes
• stimulation of endocytosis into host cells

Question 15

3 routes by which bacteria can penetrate gut epithelial layer

Answer 15

• adhering to and entering M cells –> kills by apoptosis
• adherence of fimbriae to luminal epithelial surface
• dendrites of dendritic cells between epithelial cells to breach the layer

Question 16

what are M cells

Answer 16

epithelial cells found on intestinal mucosa –> transport organisms and particles from gut lumen to immune cells across epithelial barrier (stimulate mucosal immunity)

Question 17

best mechanism of adherence

Answer 17

mediated by pili or fimbriae –> mediates adherence on host cell surface

Question 18

virulence factors that promote colonization (5)

Answer 18

• fimbriae/pili
• adhesins
• invasins
• motility
• IgA proteases

Question 19

adhesins

Answer 19

• cell surface proteins for adherece

- mediate tighter binding of bacteria to host

Question 20

invasins

Answer 20

• attach to host cell surface and cause changes in host cell cytoskeleton –> enter host
• surface proteins that provoke phagocytic ingestion of bacteria by host cell

Question 21

capsule

Answer 21

covers surface of bacteria to protect it from host’s inflammatory response-complement killing activation and phagocyte-mediated killing

Question 22

how siderophores help bacterial survival

Answer 22

• compounds that chelate iron
• excreted into medium by bacteria
• iron-siderophore complex taken up by bacteria
• make iron available to bacteria (essential for growth)

Question 23

2 possibilities for bacterial invasion

Answer 23

• immune system recognizes and destroys –> organism failed to establish itself, cannot manifest disease
• immune system fails, organism has evolved strategy for evading/suppressing host respose

Question 24

strategies for avoiding immune system

Answer 24

• against acquired immunity
• against phagocytes
• suppression of antibodies
• antioxidant enzymes
• spores
• adherence mechanisms
• toxins

Question 25

suppression of antibodies

Answer 25

- invading organism targets immune cells - prevents body from mounting a response - ex) TB reduces IL-2

Question 26

hiding inside cells

Answer 26

- do not present antigens that will evoke a response - multiply inside cells and then invade further - ex) brucella, listeria, TB infect macrophages

Question 27

anti-oxidant enzymes

Answer 27

deactivate products generated by phagocytes that normally kill bacteria

Question 28

anthrax spores

Answer 28

- soil borne, persist for a long time - can reinfect over 70 years later - unique bacilli

Question 29

exotoxin

Answer 29

- excreted by microorganism - can cause damage to the host by destroying cells or disrupting normal cellular metabolism - mostly gram + - released and act on the surface of host cells

Question 30

endotoxins

Answer 30

- part of the outer membrane of the cell wall in gram - bacteria - not secreted (structural component only) - released mainly when bacteria are lysed - trigger phagocytes to release cytokines

Question 31

inhibition of chemotaxis

Answer 31

- chemotaxis: process by which phagocytes are led to the site of infection - toxins inhibit the movement of phagocytes (staph aureus)

Question 32

inhibition of phagocytosis

Answer 32

don't present anything for phagocytes to grip onto

Question 33

killing the phagocyte

Answer 33

- release toxins that are lethal to phagocyte | - TB, strep, staph, anthrax

Question 34

colonization of phagocyte

Answer 34

- allow themselves to be phagocytized but resist being killed once inside - multiply once inside

Question 35

indirect mechanisms of tissue damage by pathogens (3)

Answer 35

- immune complexes (antigen:antibody complex) - anti-host antibody (antibody cross reacting to host) - cell-mediated immunity (t cells killing infected cells)

Question 36

superantigens

Answer 36

- cause non-specific activation of t-cells --> massive cytokine release (TNF-alpha) - shock, multiple organ failure

Question 37

antibiotic induced infections

Answer 37

- massive death of commensal organisms normally in the colon - pathogenic bacteria can take over - clostridium difficile

Question 38

clostridium perfringens

Answer 38

- opportunistic pathogen - alpha and epsilon toxins - overheating disease, pulpy kidney disease - neurologic signs

Question 39

virulent foot rot

Answer 39

- opportunistic pathogen - dissolves hoof keratin - spontaneous recovery

Question 40

lipopolysaccharide

Answer 40

- LPS is integral part of gram - bacterial membrane - lipid A portion responsible for endotoxic activity - LPS activation of macrophages

Question 41

mycobacterium bovis

Answer 41

- granulomatous lesions --> tubercles - inhaled or ingested - blocks acidification of phagolysosome - escapes phagolysosomes to replicate within host cells - impaired organ function

Question 42

mycobacterium paratuberculosis

Answer 42

- johne's disease - infected feces ingestion - enteric disease