bacteriology toxins Flashcards
endotoxin vs exotoxins
* gr +/-
* diffusible/bound
* made from?
* labile/stable?
* potency?
* pyrogenic?
* antigenic?
* synthesis
endotoxins:
* only gr -
* part of cell wall
* LPS complex
* stable
* moderate toxicity
* pyrogenic
* weakly antigenic
* synthesis encoded in chromosome
exotoxins:
* gr- and +
* diffusable
* proteins
* labile
* potent toxin
* not pyrogenic
* highly antigenic
* synthesis extrachromosomally
what is endotoxemia
the presence of endotoxin in the blood
how we describe the group of clinical signs observed when endotoxemia is present
species are variable in their susceptibility:
horses & rabbits>humans>cattle & sheep>dogs & cats
Free LPS has 20 x greater biological activity than bound LPS
It is this “free” endotoxin that can be found circulating in the blood and induces the clinical endotoxemia
When is endotoxin released?
Endotoxin is released upon Gram negative bacterial death or during proliferation/multiplication
Free LPS has 20 x greater biological activity than bound LPS
It is this “free” endotoxin that can be found circulating in the blood and induces the clinical endotoxemia
endotoxin structure
O region/antigen
* sugars project into extracellular fluid
* highly variable & antigenically specific for each bacterial strain
Core acidic polysaccharide region
* Connects O and Lipid A
* Is conserved across gram negative bacteria
* Is the region to which protective Ab may be directed
A hydrophobic Lipid A region
* Which is largely buried in the bacterial outer membrane
* Mediates most of the TOXIC EFFECTS of endotoxin
* Is conserved, but variation in number and length, saturation and position of FAs causes difference in toxicity
O region on endotoxin
- sugars project into extracellular fluid
- highly variable & antigenically specific for each bacterial strain
Core region on endotoxin
acidic polysaccharide region
* Connects O and Lipid A
* Is conserved across gram negative bacteria
* Is the region to which protective Ab may be directed
Lipid A region in endotoxin
A hydrophobic Lipid A region
* Which is largely buried in the bacterial outer membrane
* Mediates most of the TOXIC EFFECTS of endotoxin
* Is conserved, but variation in number and length, saturation and position of FAs causes difference in toxicity
effects of endotoxins
LPS read by our tissues as the very worst of bad news
When we sense LPS we are likely to turn on every defense at our disposal
IF the body’s defences to endotoxin is properly localized and regulated > responses protect the host from harmful gram negative bacterial infections
BUT IF endotoxin spills into the systemic circulation > global activation of the same inflammatory systems that are normally protective
* which may result in widespread destruction of host tissues and the clinical signs of endotoxic shock
PAMPS
pathogen associated molecular patterns
characteristic molecular changes associated with endotoxin
Phases of PAMPS
Phase I: Physical Barriers are Breached
Phase 2: Initial contact between LPS and blood
Phase 3: Macrophage activation & dependent processes
Phase 4: Neutrophil activation and dependent processes
Phase 5: Clinically apparent circulatory insufficiency
and organ damage
Death or recovery
Phase 1 PAMPS
Physical Barriers are breached
Endotoxin is ubiquitous in the environment
* Both free and as a component of Gram negative bacteria
* It normally cannot penetrate the epithelial surfaces of the skin and mucus membranes of the respiratory, urogenital and GIT tracts
* Endotoxin is restricted to the lumen of the GIT due to existence of very efficient intestinal barrier (mucosa, normal flora)
However, clinical signs of endotoxemia ensue if:
* protective integument or mucosae are damaged
* amount of endotoxin absorbed exceeds the capacity of Kupfer cells to clear it
* endotoxin is directly absorbed into the lymphatics
Diseases that can cause physical barriers to be breached by endotoxin (phase 1)
ENTERIC diseases that cause breaches:
* Bacterial enteritis (e.g. Salmonella)
* Alteration in the integrity of bowel:
* –Ischemia (bowel torsions, infarcts etc)
* –Inflammation (proximal enteritis, PHF)
* –Intraluminal acidification (grain overload)
* –Mechanical trauma (rectal perforation)
* 30-50% of all equine colic cases present with endotoxemia
NON- ENTERIC diseases that cause breaches: Gram negative infections:
* Pleuropneumonia
* Wound infections
* Placentitis/Metritis
* Septicemia
* Mastitis
* Omphalitis (umbilical cord)
Phase 2 PAMPS
Endotoxin enters bloodstream
* Endotoxin is rarely DIRECTLY toxic to mucous membranes
* Needs to get into blood stream to exert toxic effects
* When endotoxin 1st enters the blood, some is neutralized by anti-LPS antibody
* Antibody produced with previous low grade exposure
* But most forms an accumulation of endotoxin and then is bound by LPS-binding protein (LBP)
* This LPS-LBP complex in turn binds with high affinity and specificity to cell surface receptors (e.g. CD14) on macrophages
Phase 3 PAMPS
Endotoxin activates MØ
* interaction of endotoxin with macrophages (MØ) is the initiating event from which almost everything else flows in the development of the clinical signs of endotoxemia
* Binding of the LPS-LBP to the CD14 receptor causes activation of intracellular signaling pathways
Which in turn activates transcription factors
e.g., NF-kB & MAP kinase
* Macrophage activation leads to intense synthesis and secretion of a small group of EXTREMELY potent inflammatory peptides called cytokines, including chemokines
* FEVER
Phase 4 PAMPS
MØ cytokines activate neutrophils (PMNs)
* TNF and IL-1 also act on PMNs and endothelial cells to cause adhesion and margination of PMNs (leukopenia)
* BUT THEN there is a second wave of cytokines production by MØ which includes: GM-CSF, IL-8 (leukocytosis)
* PMN activation results in:
↑ sensitivity to complement products
Release of cell contents & toxic O2 metabolites onto endothelium:
↑ vascular permeability and leakage from blood vessels
damaged endothelium > procoagulant activity
Release of inflammatory mediators:
Platelet activation and aggregation
Synthesis and release of nitric oxide:
causes VASODILATION
