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Bacterial Toxins
Micro - Fundamentals
11
Mechanical Engineering
Graduate
08/27/2012

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Term
Toxin
Definition
Typical definition is a product that by itself would cause disease. Note that factors that promote colonization or thwart the immune system would not be considered toxins if they do not cause disease by themselves.
Term
Endotoxin
Definition
LPS found only on gram-negatives. Released when bacteria lyse, bind CD14 forming a complex that binds TLR-4. Activate immune system and clotting factors.
Term
Effects of endotoxin
Definition
Fever, hypoglycemia, hypotension/shock, activation of complement, impaired perfusion of organs, disseminated intravascular coagulation (DIC) resulting in occlusion of small vessels. Death may result from shock and massive organ dysfunction.
Term
Mechanism of effects of endotoxin
Definition
TLR-4 (which binds CD-14~LPS) is one of many pattern recognition receptors (PRRs) that bind pathogen associated molecular patterns (PAMPs) which stimulate cytokine production. Macrophages produce TNF and IL-1 when activated which are thought to mediate effects of endotoxin.
Term
Exotoxin
Definition
Proteins produced by bacteria that are usually secreted, but sometimes released upon lysis. Many are enzymes, all function to inhibit, destroy activity or function of a critical biological process in the host
Term
Types of exotoxins (4)
Definition
A-B subunit internalized
Single subunit internalized
Membrane-active
Superantigens
Term
A-B subunit internalized exotoxins
Definition
B (binding) subunit mediates adherence of toxin complex to host cell surface and helps transmit A subunit into cell.
A (active) subunit possess the damaging enzymatic activity. Ex: diphtheria toxin, cholera toxin, anthrax toxin.
Term
Single subunit internalized exotoxins
Definition
One subunit with enzymatic activity that causes damage. Ex: B. pertussis adenylate cyclase toxin, C. difficile cytotoxins A and B.
Term
Membrane-active exotoxins
Definition
Various types of toxins that act at the membrane such as hemolysins (oligomerize to form membrane pores), membrane lytic enzymes, Staph. aureus exfoliative exotoxin that presumably disrupts cell-cell junctions etc.
Term
Superantigens
Definition
Mediate binding of T cell to antigen presenting cell nonspecifically (by binding outside of the usual binding domain). Causes mass activation of many T cells and release of cytokine, with resulting endotoxin-like syndrome.
Term
Steps in treating toxin-mediated disease.
Definition
Identification: isolation of toxin-producing organism from patient or in some cases the exotoxin itself.
Treatment: antibiotic treatment of organism itself, sometimes may be able to neutralize the toxin itself with antitoxin serum (antibody) but is often not possible.
Prevention: some disease can be prevented by application of a toxoid (toxin rendered inactive by formalin or heat but still elicits immune memory).
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