Toxins are poisonous substances - the products of vital activity of microorganisms, possessing high molecular weight and antigenic properties.
Bacterial toxins are divided into two groups - exotoxins and endotoxins, which differ in their properties and in the nature of the action on the body.
Exotoxins are produced by a microbe in the environment, have a highly pronounced poisonousness. For example, the minimum lethal dose of native (crude) diphtheria toxin for guinea pig is 0.0002 ml, tetanus toxoid - 0.005 ml, and botulinum - 0.0001 ml. The activity of purified toxins is several hundred times higher.
The effect of exotoxins on the body manifests itself through a certain incubation period. Endotoxins act after a shorter period of time.The
Endotoxins are structural components of a bacterial cell and enter the environment only after it has been destroyed. Endotoxins are significantly inferior to exotoxins due to their toxicity. Exotoxins are thermolabile substances: most of them are destroyed at t ° 60-80 ° for 10-20 minutes. Endotoxins have a high resistance to heat: they break down at a higher temperature or with prolonged boiling. Exotoxins are less resistant to different physicochemical factors compared to endotoxins. Freezing and thawing of toxins do not have a noticeable effect on their strength. Toxins are well preserved in the dried state.
The action of formalin and heat on exotoxins deprives them of toxic properties, but retains immunogenicity. On this principle, the preparation of so-called anatoxins (see), used to prevent a number of infections, has been developed. Attempts to obtain anatoxins from endotoxins were unsuccessful. Most exotoxins are used when titrating the appropriate antitoxic sera.
A characteristic feature for exotoxins is the pronounced antigenicity - the ability to induce the formation of antibodies with a high degree of specificity when administered. This circumstance makes it possible to develop therapeutic and preventive serums against diseases caused by pathogens that produce exotoxins in production conditions.
Most exotoxins are produced by Gram-positive bacteria. However, according to a number of researchers, exotoxins are able to produce some gram-negative species (pathogens of plague , pertussis, Grigoriev-Shigi's dysentery rod).
The biological properties of a number of products of animal and vegetable origin are very close to microbial toxins (for example, plant poisons of abrin, robin, racin, animal poisons of snakes, scorpions, spiders).