Bacteriology 12: Toxins Flashcards
Toxins big 3
Evasion
Damage
Dysfunction
Exotoxins
Gram+ AND Gram- Bacteria
Released by Live Bacteria
Proteins or Polypeptides; distinct structure that differ for
toxins and bacteria
Not Pyrogenic (NO fever)
Highly antigenic
Often readily converted to toxoids
Toxin and Toxoids can induce neutralizing antibodies
Potent toxins
Some variation between species of bacteria and species of animal as to effect
Endotoxins
Gram- ONLY
Released on Cell Death
Lipopolysaccaride; same structure regardless of gram
(-) bacteria of origin
Pyrogenic (induces Fever)
Weakly antigenic
Not amenable to toxoid production
Questionable efficacy of O side chain mutants
Neutralizing antibodies not associated with natural exposure
Moderate toxins
Significant variation between species of bacteria and species of animal as to effect
Exotoxins we’ve talked about are?
P. multocida type D dermonecrotic and B. bronchiseptica dermonecrotic and osteotoxin toxins
that contribute to Atrophic Rhinitis
Staphylococci and Streptococci hemolysins that contribute to inflammation
Endotoxemia
When endotoxin gets it into blood stream
Any gram- bacteria
Species are variable in their susceptibility to endotoxemia?
HORSES AND RABBITS
–> humans
–> cattle and sheep
–> dogs and cats
Endotoxin is released upon gram- bacterial _____ or during ____________/_________________
Death
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
Each LPS molecule has _ structural domains
3
Polarpolysaccharide O-region = o Ag
-These sugars project into extracellular fluid
-This region is highly variable & antigenically
specific for each bacterial strain
Core acidic polysaccharide region
-Connects 1 & 3
-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
What are the effects of endotoxin?
Gram negative bacteria have LPS in their walls and these macromolecules are 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; we will bomb, defoliate, blockade, seal off, and destroy all tissues in the area…”
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
The characteristic molecular changes associated with endotoxin are called PAMPS
(= pathogen associated molecular patterns)
and are extremely complex
Mechanism of endotoxin
Phase 1: 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 a very efficient intestinal barrier:
-Mucosal epithelial cells and their secretions (mucus)
-Resident bacterial population
-Small amount that is absorbed is cleared by Küpfer cells in liver
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
What are common NON-ENTERIC disease that can cause breaches : gram- infections
Pleuropneumonia
Wound infections
Placentitis/Metritis
Septicemia
Mastitis
Omphalitis
What are common ENTERIC disease that can 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)
Phase 2: Endotoxin enters blood stream
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: Endotoxin activate Macrophages
The 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
Within 30 minutes of LPS binding there is production of COX-2 which causes:
- Processing of MØ plasma membrane arachidonic acid into vasoactive lipid mediators (e.g., thromboxane A2)
-Thromboxane A2 (TXA2) acts locally to cause:
–>Aggregation of platelets
–>Elaboration of additional TXA2 and serotonin
–>Initial VASOCONSTRICTION
Phase 4: Macrophages cytokines activate neutrophils (PMNs)
TNF and IL-1 also act on PMNs and endothelial cells to cause adhesion and margination of PMNs
BUT THEN there is a second wave of cytokines production by MØ which includes:
GM-CSF
IL-8
Neautralizing endotoxins
Induction or administration of antibodies to LPS
Compounds that bind and remove endotoxin from circulation or prevent it binding to inflammatory cells
Antibodies can neutralise LPS from a VARIETY of gram negative bacteria!!!
Controversial
out there but unknown how well they work
Methods of inducing or delivering anti-LPS neutralizing antibodies
Endovac-equi – LPS vaccine for active immunization
Endoserum – anti-LPS antibodies for passive administration
Fresh/frozen plasma
- Hyperimmunized equine serum to LPS available
–>Protein helps colloidal oncotic pressure
–>May also provide complement components, fibronectin, and clotting factors
Bind and/or remove Endotoxin
Polymixin B (polypeptide)
- binds lipid A and blocks interaction with CD14 and therefore activation of macrophages
- But nephrotoxic!!!
- But toxic conc. > conc. required to bind LPS
- Early use (when LPS is first circulating) more effective
Synthetic peptides that do the same thing
