Parasites way of life Flashcards
parasite life cycle components?
- Surface colonization
- Finding a nutritionally compatible niche
- Surviving host defenses
- Intracellular life
- Subverting host immune responses
- Transmission to a new host
Surface colonization by bacteria
specifity?
Preference of bacteria for particular locations in body, bacteria vary in specificity = tissue tropism
Adhesins on bacterium
Receptors on host cell
gram-negative bacteria adhesion/ intimins
- bacterial proteins on the tips of fimbriae and/or pili often interact with glycolipids and/or glycoproteins of host epithelial cells
intimins (bacterial proteins at the the cell surface) interact with their
own translocated intimin receptor (TIR): will cause signal transduction to disrupt actin polymerization and disturb the membrane
gram-positive bacteria surface colonization, usual mechanism? what molecules used?
often bind host fibronectin (epithelial cells), which binds to integrins
MSCRAMMS, SRRP
MSCRAMMS
Gram +
fibronectin binding proteins = subclass of a largefamily of bacterial adhesins
can target fibronectin, fibrinogen and collagen
many individuals in poor health and bacterial adhesion
deficient in what? result?
fibronectin-deficient
- balance shifts in favors of gram negatives
e. g. greater incidence of pneumonias caused by gramnegative bacteria
SRRP
what gram bac?
binds to?
Gram +
serine rich repeat proteins (SRRPs) (= bacterial adhesins) contain a domain of hundreds of alternating serine residues
Extend a unique non-repeat (NR) domain that mediates adhesion
NR domain binds sialic acid moieties, keratin, and other NR domains of a similar SRRP
SRRPs of oral infectious disease
species?
bind to?
SRRPs of endocardidits
species?
bind to? result of this?
Finding a nutritionally compatible niche for bacteria
Intermittent availability of food for some bacteria
e.g. intestinal bacteria
Adaptation to particular location
Surviving host defenses mechanisms
defending against complement
subverting phago
defense against complement mechanisms
masking and inhibition
Microbial mechanisms to defend against complement (4)
- polysaccharide capsule to mask surface components
- sialic acid added to the surface to inhibit complement fixation
- LPS=thick layer to prevent MAC access to the cell membrane
- production of proteases to cleave components of complement (C3b protease)
subversion of phago mechanisms
how can pathogen survive within the phago?
inhibiting phagocyte recruitment and function via C5a peptidase
Increasing cAMP to inhibitory levels within phago
killing phagocytes via leukocidins (compromise phagolysosome)
escaping ingestion via protein A- (Staphylococci and Streptococci):
surviving inside phagocytes-
inhibit lysosomal fusion with phagosome,
escape into cyto via created pores,
resist lysosomal enzymes,
inhibit phagocyte’s oxidative pathway (respiratory burst)
components of intracellular life
penetration into host cells and transmission
Penetration of nonphagocytic host cells via internalin and invasins
Some bacteria enter host cells by stimulating host cell membrane protrusion
internalins interact with host E-cadherin
invasins interact with host integrins
both interactions produce signals to disrupt actin polymerization, leading to a disrupted/rippled membrane that can lead to internalization
transmission from cell to cell
Actin-dependent intracellular motility and intercellular spread
Subverting immune responses components
immunosuppression: HIV
superantigens (diverting lymphocyte function): Ag locks TCR and MHC interaction that could be for another Ag other than the pathogen= targets other Ag
changing antigenic coats: can allow relapses with a population of the pathogen always maintained
proteolysis of antibodies
Transmission to a new host
judgment of transmission as passive or active can be arbitrary-consider effects on host
sneezing, coughing, diarrhea, insect
Specific transit forms for some pathogens
