Bacterial Pathogenicity Flashcards
Define pathogen
- Pathogen: microorganism that is able to produce disease
Define pathogenicity
- Pathogenicity: ability of microorganism to cause disease
Define virulence
- Virulence: degree of pathogenicity
Define opportunistic pathogen
- Opportunistic pathogens: bacteria that do not need to cause disease to enable transmission
Define obligate pathogen
- Obligate pathogens: require a host for survival and transmission. Usually cause disease
Define virulence factors
- Virulence factors: mechanisms to avoid host defences and multiply
What are 3 categories of factors that enable disease in a host + examples within each category
Pathogen factors
* Virulence
* Enviro stability
* Route of entry
* Infective dose
* Tropism
* Susceptibility to host defence
Host factors
* Species
* Breed
* Age
* Sex
* Genetics
* Physiologic
* Immune status
Modifying factors
* Stress
* Enviro
* Poor nutrition
* Tissue damage
* Immunosuppression
* Metabolic dysfunction
* concurrent disease
List 5 types of host defences used
- Peristalsis/ciliary movement will clear
- Commensal microbiota
- Glycoproteins
- Mucus: lysozyme/peptides/Ig/complement
- Tight junctions of epithelium
What are the 2 mechanisms of pathogenicity
invasiveness
toxogenesis
Define invasiveness
Invasiveness: ability two invade tissue
* Mechanisms for colonization: adhesins/invasins
* Ability to overcome host defence
Define toxogenesis
Toxogenesis: ability to make toxins
Define endotoxin
- Endotoxin: bacterial cell-associated substance
o Transported by blood/lymph
o Cytotoxic to cells away from original point of invasion/growth
o Mainly from gram (-)
o From cell wall (lipid A/LPS) – released when cells die and wall breaks
o Causes nonspecific signs related to inflam:
Fever/WBC change/DIC/hypotension/shock/death
Define exotoxin
- Exotoxin: make from bacterial cells and act at tissue sites away from bacteria
o Mainly from gram (+)
o Enzymes and proteins that are secreted - with specific target
o Heat sensitive
o High biological activity
Provide 2 examples of exotoxin related disease
Pyoderma in Dogs: Staphylococcus pseudointermedius exfoliating toxin
* Exotoxin: specific toxin targeting specific receptor
Enterotoxigenic enteritis: E. coli enterotoxins causing scours
* Toxin activated ion/water pump = osmotic diarrhea
* Colonize microvilli of small intestines
* Causes functional lesion – no structural lesions
What are superantigens
- Pyrogenic exotoxins made by S. aureus and S. pyogenes = superantigens
o Directly bind T cells/APC
What are the steps of pathogenesis
Establish Infection/Colonization
Evade Host Defences
List the 4 portals of entry for bacteria
Portals of Entry: urogenital/GI/resp/conjunctiva
What is the mechanism of colonization? Define the different parts.
- Receptor; carbohydrate or peptide residue on eukaryotic cell
- Bacterial ligand: adhesin (macromolecular component of bacterial cell surface)
o Ex. fimbriae
adhere to eukaryotic cell/tissue (need receptor/ligand)
What are 3 factors that adherance depends on?
- Tissue tropism
- Species specificity: infect certain species
o Enteropathogenic E. Coli K88 in pigs only - Age specificity
What is tissue tropism
- Tissue tropism: preference for tissue
What is the counter attack complex? Provide an example
Counter attack: understanding virulence mechanisms can help prevent disease
* Ex. Pigs have receptor for F4 E. coli K88 fimbrae > breed them to not have the receptor or use vaccine to make anti-F4 (fimbrae) Ig
What virulence factor allows bacteria to enter
- Invasins: factors that allow internalization of bacteria
What is the type 3 secretion system? give an example
- Type 3 secretion systems
o Many gram (-) have: deliver effector proteins
o Hijack host cell signalling
o Secretion (into ECF) or translocation (directly into host)
o Ex. Salmonella typhimurium: deliver effectors/invasins that change host actin = increases uptake in membrane vacuoles
Effector protein SopB induces enterocytes = induce transformation into M cells = increase colonization and invasion
What are spreading factors
- Spreading factors: bacterial enzymes that impact physical properties of tissue matrices/intracellular spaces = increase pathogen spread
List 4 types of spreading factors. What do they do? Which types of bacteria use them?
o Hyaluronidase: attack intracellular matrix/connective tissue (form encapsulations in matrix)
Made by streptococcus/staphylococcus/clostridia
o Collagenase: break collagen in muscles (facilitate gas gangrene)
Made by clostridium histolyticum and perfringens
o Neuraminidase: degrade neuraminic acid (aka sialic acid)
Form residue in intestinal mucus
Made by vibrio cholerae and shigella dysenteriae
o Streptokinase/Staphylokinase: kinase enzymes convert plasminogen to plasmin (digest fibrin/prevent clotting)
Made by streptococcus and staphylococcus
What are the 3 main roles of complement
tag microbes for phagocytosis,
microbial lysis (MAC),
pro-inflam
What are 3 mechanisms of complement evasion? How does it prevent complement
o Capsules: polysaccharide capsule = hide bacterial components
Prevent complement formation
o LPS: main complement target for gram (-) = can change attachment of sialic acid resides to LPS 0 antigen
Prevent MAC
o Destroy complement: extracellular enzyme (ex. Pseudomonas aeruginosa)
What are 4 mechanisms of phagocytosis resistance
o Avoid contact with phagocytes
o Prevent engulfment
o Prevent lysozyme
o Kill/Damage phagocytes
How do bacteria avoid phagocytes? Provide examples
Stay in regions where phagocytes can’t go: lumen of GII/oral cavity/urinary/mammary/kidney tubule
Hide antigenic surface
* Staphylococcus aureus: cell bound coagulase (clot fibrin on bacteria surface)
* Group A Streptococcus: hyaluronic capsule
Inhibit phagocyte chemotaxis
* Mycobacterium tuberculosis
How do bacteria prevent phagocytosis engulfment? Provide examples
Antiphagocytic molecules on surface
* S. pneumoniae/Klebsiella pneumoniae: Polysaccharide capsule
* Group A streptococcus: M protein/fimbriae
* Pseudomonas aeruginosa: Surface slime polysaccharide
* E. coli: O antigen associated with LPS (capture heavy chain of Ig in a configuration where phagocytes can’t bind)
* S. aureus:Protein A (cell bound/soluble)
3 mechanisms bacteria use to survive in phagocyte? Provide examples
Inhibit phagosome-lysosome fusion
* Salmonella/Leigonella/Chlamydiae/Mycobacterium avium paratuberculosis
Surrvivee in phagolysosome
* Bacillus anthracis/S. aureus/Coviella burnetii
Escape phagosome
* Rickettsia (make phospholipase that lyse phagosome)
Explain mechanisms bacteria use to kill phagocyte? Provide examples
Kill before engulfment
Hemolysin: extracellular enzymes made by gram (+)
* Pyogenic cocci (S. pyogenes/S. aureus)
Streptolysin: secrete by pathogenic streptococcus
* Streptolysin 0 binds cholesterol in membranes = lysosomal granules in neutrophils explode + release contents into cytoplasm
Kill after ingestion
* Mycobacteria/Brucella/Listeria
List the mechanisms bacteria use to evade humoral immunity
o Attack: Aggressive/acute attack (no time for Ig prod.)/ proteinase (degrade Ig)
o Protect: Cell wall protection: capsule/peptidoglycan/LPS
o Hide: Intracellular hiding/antigenic mimicry (campy LPS/strep M protein)
o Superantigens: divert cell immune response + make non-neutralizing Ig
List 2 mechanisms of host damage due to bacteria. What kind of damage do they do?
Direct bacterial (virulence factors): protease/hemolysin/toxin
* Cardiovascular disturbances
* Destroy blood vessel
* Diarrhea
* Disrupt NS and plasma membranes
* Inhibit protein synthesis
* shock
Induce host immunity: ROS/nitrogen species/inflammation/septic shock
