Microbial pathogenisis Flashcards
def. pathogenicity
ability of microbe to cause disease
def. virulence
traits that render micorbes pathogenic
2 general divisions of virulence
- invasion
2. host damage
4 virulence factors involving invasion
- portal of entry
- surface colonization
- surviving host defences
- portal of exit - transmission to new host
3 main sites of entry
- skin - reuires break
- mucosa
- transplants
2 ways to surface colonize
- adhesins - fimbriae, capsues
2. bind to receptors of host and transcytosis
2 general classes of host defences
- non-specific
2. specific
3 types of non-specific host defences
- barriers
- complement
- phago
2 specific host defences
- antibody mediated
2. cell-mediated
ways to survive complement (2)
- surface proteins that bind/inhibit complement
2. capsules and biofilms that mask activating substances
3 ways to survive phago
- capsules and biofilms so no access
- exotoxins kill neutrophils and macros
- intracellular survival
6 ways to survive specific defences
- immunosupression (HIV)
- diversion of lymphocyes function - superantigens
- antigenic variation - change surface antigens
- proteolysis of ABs - extracellular proteases
- prevnt opsinization - bind the Fc portions
- viral latency
5 modes of transmission
- contact (direct or indirect)
- droplet
- airborne
- vector borne
- common vehicle
4 general ways a microbe causes damage
- due to host response
- toxins
- apoptosis
- mechanical causes
potential problems from host reponse
- inflammation - prostattis
- rheumatic fever
- complement - septic shock
2 types of toxins
- exotoxins - secreted by bacteria into surronds
2. endotoxin - part of outer membrane of gram- bacteria
5 mechanisms of action of exotoxins
- help spread in tissue - break down tissues
- lyse cells - kill WBC or RBC
- block protein synthesis
- elevate/supress normal cell function
- block nerve function - most potent
what does tetanus toxin do
- travels up neuron with retrograde transport
- inhibs. release of GABA which is inhibitory neurotransmitter, hence muscle contractions
what does botulinum toxin do
- affects peripheral nerve endings
- block presynaptic Ach
- can’t move
2 ways to protect against exotoxins
- vaccinate with toxoids
2. treat with anti-toxins
what are endotoxin effects at low and high levels
low - interact with phagos to stim cytokines and cause fever
high - alarming cytokine repsonse leading to shock and intravascular coagulation
what is effect of microbes on apop
some prevent ever dying (warts) and some make cell do so prematurely
what is mechanical cause of damage
worm blockage - gross
what are 2 classifications of pathogens
- opportunistic
2. true pathogens
what are opportinitic pathogens
require some sort of break in the host defences to get in
what are true pathogens
able to cause disease despite solid defences
how does virulence factor relate to pathogens
true pathogens have more virulence factors
what is normal flora
micro-organisms that are normally found on healthy persons
4 locations to have normal flora
- skin
- resp tract
- GI
- GU
- 3 normal bact. on skin
- staphylococcus
- cornybacterium
- bacillus
- 3 normal bact. in oropharynx
- neisseria
- heamophilus
- candida
5 normal bact. in intestine
- enterococcus
- E.coli
- BActeroides
- Clostridium
- Candida
2 normal bact. in vagina
- streptococcus
2. candida
4 benefits of normal flora
- immune stimulation
- infection prevention
- human nutrition
- digestion
2 harmful effects of normal flora
- source of opportunistic infections
2. source of contaminations in tests
