Bacterial Pathogenesis Flashcards
What are some examples of bacterial virulence factors?
capsule
flagellae
pili
toxins
enzymes etc
the outcome of an interaction between host and pathogen is dependent on what?
1) the virulence of the pathogen
2) the susceptibility of the host (effectiveness of the host defences)
how do normal flora, virulent, and opportunistic pathogens differ?
what’s the most common gram negative bacilli?
e.coli
what is the most common cause of urinary tract infections?
ascending e.coli from the bowel
where do we cary staphalococci?
the anterior nostrel
what is an opportunistic bacteria?
bacteria with a low virulence that only really cause infection in patients who are immunoccompromised
what is horizontal transmission?
going across from person to person
ie. ingestion, inhalation, penetration etc
what is vertical transmission?
transplacental transmission from mother to child
typically what is transmitted by needle stick?
typically it’s a virus, but occasionally it is bacteria
how do organisms attach to the host?
bind to specific epithelium receptors - usually using fimbriae
their capsule is made to do this
what is the benefit of flagellae?
they allow for evasion of the host immune system
how do some pathogens inhibit phagocytosis?
some of them have surface components which inhibit phagocytosis
ex) capsule of S. Pneumoniae
what is the major method of immune evasion for organisms?
the capsule is the most important for attachment AND evasion
how might pathogens survive phagocytosis?
pathogens may be ingested by phagocytes but resist intracellular killing
ex) mycobacterium tuberculosis
ex) beta- haemolytic streptococci which is anti phagocytic
coagulase is an important enzyme to which pathogen?
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
how do leukocidins work?
they attack which blood cells
kill them, preventing phagocytosis and release lysosomes that cause tissue damage
how do haemolysins work?
they lyse red blood cells
(alpha = incomplete lysis
beta = complete lysis)
how does collagenase work?
helps bacteria spread, breaks down collagen found in many connective tissues
what pathogen produces urease?
Helicobactor pylori
what is the dfference between endotoxin and exotoxins?
endotoxin = released after death of the bacteria
exotoxins = secreted by living cells
which pathogen releases endotoxin before it’s died?
Neisseria meningitidis
- they shed their outer coat like a snake and therefore release some endotoxin -
what is the host response to endotoxin?
severe inflammation
- fever
- complement activation
- platelet count
- septic shock
ex) caused by E. coli and Neiseria
What is the toxic component of endotoxin?
toxicity largely due to the lipid A portion of lipopolysaccharide component of the outer membrane of Grame negative bacteria
How are exotoxins released?
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
what are the local and distal effects of exotoxins?
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*
if you ingest a dead organism, can it still cause disease?
yes.
though an organism can be dead, you’re injesting the toxins so it could still cause disease
what does cytotoxin do?
kills cells
what do enterotoxins do?
effect the GI tract cells
what are superantigens?
secreted proteins (exotoxins)
non-specific activation of T cells resulting in polyclonal T cell activation and massive cytokine release
what are some factors that might increase host susceptability to infection?
- extremes of age
- diabetes mellitus
- immunosuppression
- major break in skin/mucosa
- prosthetic materia (IV lines, catheters, ventilation etc)
- antibiotic therapy
- anatomical abnormality
