medical microbio: pathogenesis

Question 1

infection

Answer 1

growth of microbes that are not normally present in the host (regardless of whether or not the host is harmed)

Question 2

disease

Answer 2

damage or injury that impairs regular host functions

Question 3

pathogen

Answer 3

a microbe that is able to cause disease

Question 4

opportunistic pathogen

Answer 4

a microbe that causes disease only in the absence of normal host resistance:

ex. streptococcus pneumoniae- causes pneumonia in immunocompromised patients
ex. e.coli-causes urinary tract infections when bacteria from feces are moved into the urethra

Question 5

pathogenicity

Answer 5

the ability to cause disease

Question 6

virulence

Answer 6

the severity of the disease that is caused

• often given as an LD50 value
• number of cells of a pathogen (or dose of a toxin) that will cause death in 50% of infected animals
  ex. streptococcus pneumoniae - LD50 ~50 cells
  ex. salmonella enterica- LD~5000 cells

Question 7

pathogenesis

Answer 7

the precess by which a disease develops

*steps that lead to an infection and tissue damage

Question 8

virulence factors

Answer 8

genetically encoded traits that contribute to a pathogen’s ability to cause disease

Question 9

adherence

Answer 9

the ability of a pathogen to stick to a surface and begin colonization

Question 10

non-covalent adherence factors

Answer 10

ex. capsules and slime layers
- streptococcus mutans uses slime layer to stick to teeth and form a biofilm
- streptococcus pneumoniae uses capsule to stick to cells in the lungs
- also protects the cell from phagocytes

Question 11

other adherence factors

Answer 11

-adhesins- specific surface molecules that allow selective adherence to particular cell types

Question 12

examples of adhesins

Answer 12

• strains of enterotoxigenic E.coli produce fimbriae and can adhere specifically to cells in teh small intestine
• Neisseria gonorrhoeae produces fimbriae that allow it to attach to mucosal epithelial cells
• retract to bring bacteria close to the membrane
• opa proteins then specially attach to certain receptors on the host cell

Question 13

some pathogens can colonize and grow on the surface of tissues others need to _______

Answer 13

invade tissue

Question 14

invasiveness

Answer 14

-the ability of a pathogen to enter into host cells or spread through tissues

Question 15

virulence factors that promote invasiveness

Answer 15

• siderophores
• exoenxymes
• invasins

Question 16

siderophores

Answer 16

iron binding molecules

• host proteins transferrin and lactoferrin- sequester iron, making it unavailable for microoganisms
• limits the growth of invaders
• siderophores rip iron out of tissues to be used by bacteria

Question 17

exoenzymes

Answer 17

• excreted by bacteria to degrade host tissues
• hyaluronidase
• collagenase
• proteases, nucleases and lipases
• fribrinolysin
• coagulase

Question 18

hyaluronidase

Answer 18

hydrolyzes hyaluronic acid (cement that holds animal cells together)

Question 19

collagenase

Answer 19

degrades collagen (structural component of connective tissue)
allows pathogen to spread through tissues

Question 20

proteases, nucleases and lipases

Answer 20

degrade host macromolecules

Question 21

fibrinolysin

Answer 21

dissolves fibrin clots

*ex. streptococcus pyogenes makes streptokinase

Question 22

coagulase

Answer 22

induces fibrin clots

ex. staphlococcus aureus produces coagulase to protect it from phagocytes
* keeps staph infections localized

Question 23

invasins

Answer 23

proteins that allow bacteria to invade and enter directly into host cells

Question 24

listeria monocytogenes

Answer 24

• invasins
• non lactic acid, non pore forming psychrotolerant (grows best at lowe temp) member of the firmicutes
• produces invasins that promote phagocytosis by macrophages
• hijacks the cytoskeleton to escape the phagolysosome
• spreads from cell to cell- avoiding humoral immune response

Question 25

some pathogens remain localized at the site of infection while others _____

Answer 25

spread

Question 26

bacteremia

Answer 26

bacteria in the blood | can be carried to different organs and tissues

Question 27

septicemia

Answer 27

bacteria multiplying in the blood (blood borne systemic infection) -can lead to sepsis

Question 28

sepsis

Answer 28

widespread systemic inflammation

Question 29

septic shock

Answer 29

can be caused by gram negative bacteria (gram negative sepsis) -also by gram positives : staphylococci and enterococci

Question 30

exotoxins

Answer 30

proteins released by growing bacteria * inhibit host cell function (or kill host cells) * usually heat labile * can be extremely toxic

Question 31

bacillus anthracis

Answer 31

- exotoxins - several virulence factors: capsule, exoenzymes and the anthrax toxin * interferes with the immune response and kills macrophages

Question 32

there are three categories of exotoxins

Answer 32

cytoxins AB toxins superantigens

Question 33

cytotoxins

Answer 33

``` disrupt cytoplasmic membrane integrity cell lysis and death -hemolysins -lecithinase or phospholipase -leukocidins ```

Question 34

hemolysins

Answer 34

lyse many cells (not just red blood cells) ex. streptococcus pyogenes - produces streptolysin sterols in the cell membrane

Question 35

lecithinase or phospholipase

Answer 35

dissolves membrane lipids - ex. clostridium perfringens - alpha-toxin (gas gangrene)

Question 36

leukocidins

Answer 36

destroy white blood cells ex. staphylcoccus aureus - staphylococcal alpha-toxin toxin subunits insert into the membrane and oligomerize to form a heptamer a membrane spanning pore cell contents leak out and the cell dies

Question 37

AB toxins

Answer 37

two subunits : active subunit and binding subunit ex.diphtheria toxin (corynebacterium diphtheriae) subunit B- specifically binds to a protein on animal cells subunit A- then moves across the membrane *interferes with protein synthesis -gene for diphtheria toxin is not encoded on the chromosome, but instead on a virus

Question 38

other AB toxins

Answer 38

tetanus, botulism and cholera toxins

Question 39

superantigens

Answer 39

- activate T cells to elicit an extreme immune response - bind to MHC molecules and TCRs outside the antigen bind sites - bridge the gap and mimics proper antigen presentation - huge number of T cells can be activated - T cells produce cytokines - extreme immune response - extreme fever, systemic inflammation, shock, death ex. staphylococcus aureus's toxic shock syndrome toxin

Question 40

endotoxins

Answer 40

lipopolysaccharide from the gram negative outer membrane - toxic part is lipid A -only released when the cells die - generally considered less toxic than exotoxins (need a lot to cause symptoms)

Question 41

salmonellosis

Answer 41

food borne illness endotoxin -salmonella colonizes the intestine-multiply to a huge number of bacteria *as those bacteria die, they release endotoxin *fever, diarrhea, generalized inflammation

Question 42

gram negative species

Answer 42

endotoxins - gram negative bacteria multiply in the blood - killed by immune system, releasing endotoxin - massive inflammation leads to septic shock an death