Bacterial Virulence Mechanisms Flashcards
host-pathogen relationship
*dynamic relationship, each modifying the activities and functions of the other
*outcome is dependent on:
-virulence of the pathogen
-relative degree of susceptibility or resistance of the host
pathogenesis
ability of an agent of infection to produce disease
virulence
an agent of infection’s degree of pathogenicity
*how effectively it causes the disease
*the severity of the disease
virulence mechanisms
genetic or biochemical features which allow an organism to produce disease
pathogens must be able to accomplish the 5 requirements for infection:
- entry
- colonization
- immune evasion
- propagation
- transmission
portals of entry for pathogens
*mucus membranes
*skin
*parenteral (needles, bites, maternal-neonatal)
LD50
lethal dose required to kill 50% of experimentally inoculated test animals
ID50
infectious dose required to cause disease in 50% of inoculated test animals
which pathogen has a very HIGH ID50
vibrio cholera
(requires a lot of vibrio to become infected)
what pathogen has a really LOW ID50
shigella
(does not require very much shigella to become infected)
quorum sensing
*organisms sense and respond to their environment (produce, release, and sense extracellular signals to regulate gene expression)
*cell-to-cell communication
quorum sensing in gram NEGATIVE bacteria
*use acyl-homoserine lactones (AHL’s)
*diffuse freely through bacterial membrane
quorum sensing in gram POSITIVE bacteria
*use processed oligo-peptides
*two-component system: membrane-bound sensor kinase receptors and cytoplasmic transcription factors that direct gene expression
pathogenicity islands
*virulence genes in CLUSTERS (present in pathogens, absent in benign relatives)
*pick up genes from environmental gene pool by horizontal transfer
*large, distinct chromosomal regions
colonization by an organism
*the initial establishment of an organism within a particular habitat or of a colony at a particular site
*usually colonize sites that connect to the external environment
*often requires:
-IgA protease
-motility
-adherence
-biofilm production
IgA protease
-secretory IgA is the principal immunologic defense of respiratory and other mucosal surfaces in the body
***IgA protease causes LYSIS of IgA, allowing adherence of the organism to the mucus membrane
flagella
*motility
*can function as adhesins
*flagellin or FliC, filament forming component of bacterial flagella
type IV pili
*filaments at the poles of bacilli
*allow for gliding motility along a solid surface
*pili are extended and attach to a surface and then retract (causing a twitching motility) or can slingshot
examples of adhesins (virulence factors)
fimbria/pili & MSCRAMMS
fimbria
*adhesive hair-like structures extending from surface
*usually binds to a specific sugar on the cell surface (the adhesin in LECTIN)
P fimbria in E. coli
*virulence factor found in a pathogenicity island of uropathogenic E. coli
*binds to Gal-Gal on uroepithelial cells
*this is the most common cause of UTIs in the world
MSCRAMMs (microbial surface components recognizing adhesive matrix molecules)
*proteins that bind components of the ECM of epithelial cells, such as fibronectin, collagen, or laminin
*secreted by staph, strep, and others
biofilms
*irreversibly attach to a surface and produce extracellular polymers (matrix formation)
*provides antimicrobial resistance
*ALL bacteria CAN form biofilms, but some are really good at it
type III secretion systems (T3SSs)
*complex bacterial structures in gram NEGATIVE pathogens for injecting effector proteins directly into the host cell
*effector proteins commonly interfere with host cell cytoskeleton to promote attachment and invasion, create cytotoxicity and barrier dysfunction, and block immune system
