Mechanisms of infection :) Flashcards
what are pathogens
disease causing organisms that are fully virulent
what do pathgens show
clonality
reproduction -asexual
each cell has a similar capability
what are opportunistic pathogens
possess soem virulence factors
often commensals
aim of pathgen
reproduction and maintenance of its genes in envrionemtn
what are seroconverts
those who can make antibodies agains the pathogens
routes of transmission
aerosols foetal oral spread venereal spread vector vertebrate reservoir vector vertebae
vertical transmission
between generations e.g. through placenta
what is an infectious dose
have to have enough bacteria that will survive to infect
requirement for infection
adhere to susceptible cell
grow in/on host
evade host defenses
examples of bacterial appendages
pilli
what are bacterial capsules made of
polysaccharides
bind to artificial surfaces and tooth pellicles (important in biofilm formation)
what can bacteria bind to
surface proteins/glycoprotiens
e.g. HIV binds to CD4
biofilm formation
primary colonisation of surface
secondary colonisation by extracellular polysaccharide and cell interactions
what are the gradients within the plaque community
towards edge more active
what can aid colonisation
motility i.e. flagellum
what can flagellum help with
penetrate mucous blanket
penetrate intercellular junctions
colonisation of catheters
formation of pedestals
1) Bacteria sticks to cell
2) retracts the cells
3) needles stick out
4) send proteins out through the needles
5) form a hole to send more proteins
6) proteins sit in the membrane
7) Then the bacteria can sit in the membrane
8) Sends in more protein, causes actin polymerisation (cytoskeleton)
9) Pellicle is formed
how can bacteria manituplate the host
manipulate the endocytosis system of cells
bind receptors using pili
pedestal formed in intestinal brush border
then inject cell effectors using section needles
invasion of cell steps
1) Attaches
2) Sends needle inside cytoskeleton
3) Uses the vesicle to go inside
4) pH changes
5) triggers organism to send out another needle
6) Manipulates vesicle to make home for itself
7) Then divides
summary of colonisation
- Transmission by aerosol, direct contact, wound/infect
- Attachment by fimbriae, polysaccharide, protein adhesion
- Motility aids colonisation
- Invade by subversion of endocytosis system
complement involved in invasion
deposits on surface
become activated by antigens
makes membrane attack complement
bacterial cell then burst
evasion of complemtn
gram -
LPS forms a brush border preventing proteins getting to the cell membrane
gram +
capsules able to stop deposition on surface of the cell
normal IgA fuction
non complement activated cell M cell detects pathogen - T cell and B cell activation to make IgA colecuels IgA molecules are then sent out protect from adhesion
soem bacteria are able to chop up IgA
subverting phagocytosis
toxis evade phagocytosis (capsule exclusion) avoid killing within a phagosome
how do toxins evade defences
toxins can target leucoidins
kills phagocytes
how can you avoid killing within a phagosome
escape from phagosome
resist lytic enzymes
inhibit generation of superoxide or degrafde them
what does tuberculosis do
evades killing
surpasses immune responcec
multiplies in macrophages
subverting t cells
incapacitate t cells
- infects and destroys CD4 and T cells
secret agent methods of evasion
surface antigen variation molecular mimicry infection of privleged sites decoys:smokescreens degrade or inhibit complement
surface antigen variation
change antigens to evade immune system
molecular mimicry
coat with host protein
incorporation of silica acid into LPS on surface
infection of privileged sites
not easily detected in areas with less immune cells
decoys/smokescreen
bacteria may send out false messages
bind to antibodies/antigens to occupying them to give more time to run away
degraded inhibit complement
intercept codes and misinformation
give more time for colonisation, adhesion or infection
force fields
organisms produce urease
acts as protective cloud during transit to gastric mucin layer
take the urea and chop it up into amminoia and CO2
