Parasites way of life

Question 1

parasite life cycle components?

Answer 1

1. Surface colonization
2. Finding a nutritionally compatible niche
3. Surviving host defenses
4. Intracellular life
5. Subverting host immune responses
6. Transmission to a new host

Question 2

Surface colonization by bacteria

specifity?

Answer 2

Preference of bacteria for particular locations in body, bacteria vary in specificity = tissue tropism

Adhesins on bacterium
Receptors on host cell

Question 3

gram-negative bacteria adhesion/ intimins

Answer 3

1. 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

Question 4

gram-positive bacteria surface colonization, usual mechanism? what molecules used?

Answer 4

often bind host fibronectin (epithelial cells), which binds to integrins
MSCRAMMS, SRRP

Question 5

MSCRAMMS

Answer 5

Gram +
fibronectin binding proteins = subclass of a largefamily of bacterial adhesins
can target fibronectin, fibrinogen and collagen

Question 6

many individuals in poor health and bacterial adhesion

deficient in what? result?

Answer 6

fibronectin-deficient

• balance shifts in favors of gram negatives
  e. g. greater incidence of pneumonias caused by gramnegative bacteria

Question 7

SRRP
what gram bac?
binds to?

Answer 7

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

Question 8

SRRPs of oral infectious disease
species?
bind to?

Answer 8

Question 9

SRRPs of endocardidits
species?
bind to? result of this?

Answer 9

Question 10

Finding a nutritionally compatible niche for bacteria

Answer 10

Intermittent availability of food for some bacteria
e.g. intestinal bacteria
Adaptation to particular location

Question 11

Surviving host defenses mechanisms

Answer 11

defending against complement

subverting phago

Question 12

defense against complement mechanisms

Answer 12

masking and inhibition

Question 13

Microbial mechanisms to defend against complement (4)

Answer 13

1. polysaccharide capsule to mask surface components
2. sialic acid added to the surface to inhibit complement fixation
3. LPS=thick layer to prevent MAC access to the cell membrane
4. production of proteases to cleave components of complement (C3b protease)

Question 14

subversion of phago mechanisms

how can pathogen survive within the phago?

Answer 14

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)

Question 15

components of intracellular life

Answer 15

penetration into host cells and transmission

Question 16

Penetration of nonphagocytic host cells via internalin and invasins

Answer 16

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

Question 17

transmission from cell to cell

Answer 17

Actin-dependent intracellular motility and intercellular spread

Question 18

Subverting immune responses components

Answer 18

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

Question 19

Transmission to a new host

Answer 19

judgment of transmission as passive or active can be arbitrary-consider effects on host
sneezing, coughing, diarrhea, insect
Specific transit forms for some pathogens