Bacterial Pathogenesis

Question 1

What are some examples of bacterial virulence factors?

Answer 1

capsule

flagellae

pili

toxins

enzymes etc

Question 2

the outcome of an interaction between host and pathogen is dependent on what?

Answer 2

1) the virulence of the pathogen
2) the susceptibility of the host (effectiveness of the host defences)

Question 3

how do normal flora, virulent, and opportunistic pathogens differ?

Question 4

what’s the most common gram negative bacilli?

Answer 4

e.coli

Question 5

what is the most common cause of urinary tract infections?

Answer 5

ascending e.coli from the bowel

Question 6

where do we cary staphalococci?

Answer 6

the anterior nostrel

Question 7

what is an opportunistic bacteria?

Answer 7

bacteria with a low virulence that only really cause infection in patients who are immunoccompromised

Question 8

what is horizontal transmission?

Answer 8

going across from person to person

ie. ingestion, inhalation, penetration etc

Question 9

what is vertical transmission?

Answer 9

transplacental transmission from mother to child

Question 10

typically what is transmitted by needle stick?

Answer 10

typically it’s a virus, but occasionally it is bacteria

Question 11

how do organisms attach to the host?

Answer 11

bind to specific epithelium receptors - usually using fimbriae

their capsule is made to do this

Question 12

what is the benefit of flagellae?

Answer 12

they allow for evasion of the host immune system

Question 13

how do some pathogens inhibit phagocytosis?

Answer 13

some of them have surface components which inhibit phagocytosis

ex) capsule of S. Pneumoniae

Question 14

what is the major method of immune evasion for organisms?

Answer 14

the capsule is the most important for attachment AND evasion

Question 15

how might pathogens survive phagocytosis?

Answer 15

pathogens may be ingested by phagocytes but resist intracellular killing

ex) mycobacterium tuberculosis
ex) beta- haemolytic streptococci which is anti phagocytic

Question 16

coagulase is an important enzyme to which pathogen?

Answer 16

staphoreus.

• when coagulase is genetically removed from the organism, it is almost entirely avirulent
• coagulase cuases blood to coagulate and the clots protect the bacteria from phagocytosis and other host defences

Question 18

how do leukocidins work?

Answer 18

they attack which blood cells

kill them, preventing phagocytosis and release lysosomes that cause tissue damage

Question 19

how do haemolysins work?

Answer 19

they lyse red blood cells

(alpha = incomplete lysis

beta = complete lysis)

Question 20

how does collagenase work?

Answer 20

helps bacteria spread, breaks down collagen found in many connective tissues

Question 21

what pathogen produces urease?

Answer 21

Helicobactor pylori

Question 22

what is the dfference between endotoxin and exotoxins?

Answer 22

endotoxin = released after death of the bacteria

exotoxins = secreted by living cells

Question 23

which pathogen releases endotoxin before it’s died?

Answer 23

Neisseria meningitidis

• they shed their outer coat like a snake and therefore release some endotoxin -

Question 24

what is the host response to endotoxin?

Answer 24

severe inflammation

• fever
• complement activation
• platelet count
• septic shock
  ex) caused by E. coli and Neiseria

Question 25

What is the toxic component of endotoxin?

Answer 25

toxicity largely due to the lipid A portion of lipopolysaccharide component of the outer membrane of Grame negative bacteria

Question 26

How are exotoxins released?

Answer 26

released from replicating bacterial cells and host cells that are lysed by host defences

OR

released because of th emechanism of certain antibiotics ex) beta-lactam antibiotics

Question 27

what are the local and distal effects of exotoxins?

Answer 27

local = tissue necrosis (gangrene),

distal = can act at sites far away for the site of bacterial growth

*some bacteria toxins can also act at the site of colonisation and play a role in invasion*

Question 28

if you ingest a dead organism, can it still cause disease?

Answer 28

yes.

though an organism can be dead, you’re injesting the toxins so it could still cause disease

Question 29

what does cytotoxin do?

Answer 29

kills cells

Question 30

what do enterotoxins do?

Answer 30

effect the GI tract cells

Question 31

what are superantigens?

Answer 31

secreted proteins (exotoxins)

non-specific activation of T cells resulting in polyclonal T cell activation and massive cytokine release

Question 32

what are some factors that might increase host susceptability to infection?

Answer 32

• extremes of age
• diabetes mellitus
• immunosuppression
• major break in skin/mucosa
• prosthetic materia (IV lines, catheters, ventilation etc)
• antibiotic therapy
• anatomical abnormality