Types of toxins

Damage to the host may arise in two ways. First, multiplication of the microorganisms may cause mechanical damage to the tissue cells through interference with the normal cell metabolism, as seen in viral and some bacterial infections. Second, a toxin associated with the microorganism may adversely affect the tissues or organs of the host. Two types of toxins, called exotoxins and endotoxins, are associated with bacteria. 

This bacterium can produce numerous types of toxins that cause a range of medical problems. The most potent toxin of C. perfringens is the alpha toxin — the one most likely to be used by terrorists. It would be lethal by aerosol delivery. 

Figure 1 The mode of action for bacterial AB-type exotoxins. AB-toxins are enzymes that modify specific substrate molecules in the cytosol of eukaryotic cells. Besides the enzyme domain (A-domain), AB-toxins have a binding/translocation domain (B-domain) that specifically interacts with a cell-surface receptor and facilitates internalization of the toxin into cellular transport vesicles, such as endosomes. In many cases, the B-domain mediates translocation of the A-domain into the cytosol by pore formation in cellular membranes. By following receptor-mediated endocytosis, AB-type toxins exploit normal vesicle traffic pathways into cells. One type of toxin escapes from early acidified endosomes (EE) into the cytosol, thus they are referred to as short-trip-toxins . In contrast, the long-trip-toxins take a retrograde route from early endosomes (EE) through late endosomes (LE), trans-Golgi network (TGN), and Golgi apparatus into the endoplasmic reticulum (ER) from where the A-domains translocate into the cytosol to modify specific substrates.

The risk of CFP and the severity of disease symptoms may be associated with population sensitivity to the disease and a variety of other conditions. These conditions include the location where the fish was caught, the amount and parts of the fish eaten, fish species, fish size, seasonal fish distribution patterns, types of toxins present, and local ecologic reef disturbances (Lange et ah, 1992). 

Biological methods Despite ethical objections, a biological method employing mice is still applied due to its sensitivity. It enables detection of the presence and type of toxin, and can be used for food as well as in serum, vomit, and stool samples. 

Selection pressure from this type of toxin would be even less. 

Species Composition Mineral group Toxic elements Type of toxin... 

The potency of an immunotoxin is dependent on the biochemical properties of both the antibody and toxin moieties. Of paramount importance are the characteristics of the target antigen and the antibody affinity for that antigen, rate of internalization into the cell, as well as the efficiency of the intracellular processing and the type of toxin. 

Freshwater cyanobacteria Microcystis, Oscillatoria, Ana-baena, and Nostoc produce several types of toxins, among which the most commonly detected are the hepatotoxic peptides microcystins. The general structure of the microcystins is cyclo-(D-Ala -X -D-MeAsp -Z -Adda -D-Glu -Mdha ), in which X and Z represent variable L-amino acids, D-MeAsp is D-eryf/iro-p-methylaspartic acid, Mdha is A-methyldehydroalanine, and Adda is the unusual C20 amino acid, (25,35,85,95)-3-amino-9-meth-oxy-2,6,8-trimethyl-10-phenyldeca-4( ),6( )-dienoic acid (Fig. 1). The structural differences in the microcystins mainly depend on the variability of the two L-amino acids (denoted X and Z), and secondarily on the methylation or demethylation of D-MeAsp and/or Mdha. More than 60 microcystins have been isolated from bloom samples and isolated strains of cyanobacteria. 

In vivo and in vitro toxin-induced model studies of PD indicate either apoptosis or necrosis depending on the particular type of toxin to which the animal or culture system is exposed. Most in vivo and in vitro DA- or 6-OHDA-exposure experiments suggest an apoptotic form of cell death, whereas MPP+/MPTP indicate necrotic cell death (130,131). The pesticide rotenone has been implicated inboth apoptotic and necrotic cell death (132-134). 

Toxins present a variety of both incapacitating and lethal effects. General types of Toxins include those that disrupt the nervous system (neurotoxins), destroy or damage tissue (cytotoxins) or cause the body to release excessive, and therefore harmful, amounts of chemicals that are normally produced by the body (biomediator Toxins). Toxins may produce effects that are a combination of these general categories. 

These venoms are a rapid-acting mixture of various types of toxins including neurotoxins, cardiotoxins, and cytotoxins. 

A modified version of the Computer Automated Structure Evaluation (CASE) program has been successfully applied to the study of the neurotoxic and cytotoxic activity of the snake venom toxins. The program identified the sites that seem to be the most relevant to the activity of these two classes of peptides. The knowledge of the three dimensional structure of these peptides together with the relevant fragments selected by the CASE program helped to clarify the differences between the activity of each type of toxin. 

Type of Toxin Means of ID Symptoms in Man Effects on Man Rate of Action How Normally Disseminated Protection Required Decontamination... 

Microcystin. An example of this type of toxin is microcystin (produced by blue-green algae), which binds covalently to a phosphatase inside liver cells this toxin does not damage other cells of the body. Unless uptake of the toxin by the liver is blocked, irreversible damage to the organ occurs within 15 to 60 minutes after exposure to a lethal dose. When this happens, the tissue damage to the liver is so severe that therapy may have little or no value. For microcystin, unlike most toxins, the toxicity is the same, no matter what the route of exposure. 

---