Causative agent of anthrax

Anthrax is an acute infectious disease of humans and animals (domestic and wild).

The Russian name of the disease was given by SS Andrievsky in connection with a major epidemic in the Urals in the late 18th century. In 1788, with the heroic experience of self-poisoning, he proved the identity of anthrax of man and animals and finally confirmed its nosological independence. The causative agent Bacillus anthracis was repeatedly described by various authors (Pollender A. .. 1849, Dalen C., 1850, Brown F., 1854), but his etiological role was finally established by R. Koch (1876) and L. Pasteur (1881) .

B. Anthracis (genus Bacillus) belongs to the family Bacillaceae (class Bacilli). It is a large stick with a length of 5-8, sometimes up to 10 microns, with a diameter of 1.0-1.5 microns. The ends of the living rods are slightly rounded, they are as if cut off and slightly concave with the dead. Sticks in smears are arranged in pairs and very often - chains, especially long on nutrient media, resembling a bamboo cane. Sibiriazvennaya stick is well-colored by all aniline dyes, Gram-positive. It has no flagellum, it forms spores, but only outside the human or animal body in the presence of oxygen and a certain humidity. The temperature optimum for sporulation of 30-35 ° С (below 12 ° С and above 43 ° С does not occur), spores are located centrally, their diameter does not exceed the diameter of the bacterial cell.The formation of spores occurs in cases when bacteria are deficient or sources of energy , or amino acids or bases, since these sources of bacteria are present in the blood and tissues, there is no spore formation in the body .The causative agent of anthrax forms a capsule, but only in the animal or human body, on nutrients (on media containing blood or serum) Capsule formation of pathogenic bacteria is a protective mechanism It is induced by factors contained in blood and tissues, so capsules are formed when bacteria are in the body or when grown on media with blood, plasma or The content of G + C in DNA varies within the range of 32-62 mol% (for the genus as a whole).

The causative agent of anthrax is aerobic or facultative anaerobic. The temperature optimum for growth is 37-38 ° C, the pH of the medium is 7.2-7.6. To nutrient medium is undemanding. On dense media forms characteristic large matte rough R-shaped colonies. The structure of the colonies, due to the chain-like arrangement of the rods, which form strands extending from the center, resembles curls or lion's mane (Fig. 98). On agar containing penicillin (0.05-0.5 U / ml), after 3 hours of growth, the bacilli break down into separate beads, arranged in a chain, forming the phenomenon of a "pearl necklace". In the broth, a stick in the R-form grows on the bottom, forming a precipitate in the form of a cotton wool, while the broth remains transparent. B. Anthracis is virulent in the R-form, it changes its virulence upon transition to the S-form. Such sticks on a dense medium form round, smooth colonies with even edges, and in broth - uniform turbidity. In this case, the sticks lose the ability to be placed in strokes of the chains and take the form of coccobacteria, located in clusters.

B. Anthracis is quite active biochemically: it ferments glucose, sucrose, maltose, trehalose, forms sucrose, glucose, sucrose, coagulates milk and peptonizes it, catalase positive, has nitrate reductase. When sowing with a prick in a column of 10-12% meat-peptone gelatin causes a layer-by-layer dilution of it.

To distinguish B. Anthracis from other species of Bacillus use a complex of features.

[1], [2], [3]

Antigenic structure of the causative agent of anthrax

The causative agent of anthrax has somatic antigens and capsular antigen of protein nature (composed of D-glutamic acid), formed mainly in the animal and human body. The somatic antigen of the polysaccharide nature is heat-stable, long-lasting in the external environment and in the corpses of animals. On his discovery, the diagnostic reaction of Ascoli thermocyclization was based. Sibiriazvennaya bacillus also has antigens common to the genus Bacillus.

[4], [5], [6],

Pathogenicity factors of the causative agent of anthrax

The most important factor in the virulence of the anthrax is the capsule. Loss of the capsule leads to loss of virulence. The capsule protects B. Anthracis from phagocytosis. Another important virulence factor that is responsible for animal death is a complex toxin complex containing 3 different components: factor I, consisting of protein and carbohydrate; and two factors of a purely protein nature (factors II and III). Synthesis of complex toxin is controlled by plasmid pXOl with a mass of 110-114 MD. In the plasmid pXOl there are three genes that determine the synthesis of the main components of exotoxin:

• Swa - puff factor gene (PF);
• pag gene - protective antigen (PA);
• lef - lethal factor (LF) gene.

The product of the sua (OP) gene is adenylate cyclase, which catalyzes the accumulation of cAMP in eukaryotic cells. The puffiness factor causes an increase in vascular permeability.

The protective antigen induces the synthesis of protective antibodies (however the most immunogenic is a complex of all three components of a detoxified toxin), the lethal factor causes the death of animals. All three components of the toxin act synergistically. Synthesis of the capsule of anthrax bacillus is also controlled by plasmid pX02 with a mass of 60 MD.

Resistance of B. Anthracis

In vegetative form, the causative agent of anthrax has the same degree of resistance to environmental factors and chemicals as other bacteria without bacteria, at temperatures above 75 ° C perish in 5-10 minutes, in corpses of animals under the influence of the products of the life activity of putrefactive bacteria - through a few days. Spores of the same anthrax are extremely resistant: tens of years are left in the soil, for several years in the water, they die after 20 days or more under direct sunlight, they are destroyed during boiling for 45-60 minutes, with autoclaving at 110 "C - After 5 minutes, dry heat (140 ° C) is kept for up to 3 hours. Spores persist for a long time in the wool and skins of animals used for various dressings and in salted meat.

Epidemiology of anthrax

The main source of anthrax are diseased herbivores. During the entire period of illness, they excrete the pathogen with urine, excrements and saliva into the soil, infecting it, so the soil, especially rich in organic substances, becomes an additional reservoir of the pathogen. Infection of animals occurs mainly alimentary (through food and drinking water, infected with spores), less often - transmissible - through the bites of flies, ticks, flies, which carry the pathogen from sick animals, corpses and from infected objects of the environment; very rarely - by air. When direct contact from a sick animal to a healthy agent is not transmitted.

Infecting a person with anthrax occurs with direct contact with the corpses of animals, when cutting carcasses of animals that have been forcibly killed, when caring for sick animals, when eating meat or meat products obtained from sick animals, in contact with wool, skins, skin, bristles, infected pathogens or his disputes. Infection of a healthy person from a patient occurs extremely rarely.

The entrance gates of infection are the skin and mucous membranes of the intestinal tract and respiratory tract. In accordance with the entrance gates, the human anthrax disease proceeds in the form of cutaneous (most often, up to 98% of all cases of the disease), intestinal or pulmonary forms. The incubation period varies from a few hours to 6-8 days, most often 2-3 days. The cutaneous form manifests itself in the form of an anthrax carbuncle, which is usually localized on exposed parts of the body (face, neck, upper limbs), less often - on body parts covered with clothing. Carbuncle - a kind of focus of hemorrhagic necrosis, on the top of which a bubble with serous-bloody contents or a dense black-brown color of a scab is formed. The skin and subcutaneous tissue of the carbuncle and around it are swollen, impregnated with serous bloody exudate, but abscesses and abscesses are usually not observed. In inflamed tissues and exudate - a large number of bacilli, surrounded by a capsule.

With intestinal form there is a general intoxication with catarrhal and hemorrhagic manifestations from the gastrointestinal tract (nausea, vomiting with blood, bloody diarrhea, abdominal pain and lower back). The disease lasts 2-4 days and most often ends in death.

The pulmonary form of anthrax is extremely rare and proceeds according to the type of bronchopneumonia with deep general intoxication, chest pain, general malaise, fever, cough with sputum discharge, initially mucous, then bloody. Death occurs on the 2-3rd day. As a rule, all forms of anthrax are accompanied by a high temperature (39-40 ° C). The most severe is anthrax in septic form, which can be both primary and consequence of complication of another form of the disease. It is characterized by an abundance of hemorrhagic manifestations and the presence of a large number of pathogens in the blood, cerebrospinal fluid and in a number of organs of the sick person. Diseases of anthrax among people are sporadic.

Postinfectious immunity is associated with the appearance of antitoxins and antimicrobial (protective) antibodies.

[7], [8], [9], [10], [11], [12],

Laboratory diagnosis of anthrax

The material for the study is: with dermal form - the contents of the vesicles, the carbuncle or ulcer being separated; at intestinal - excrement and urine; with pulmonary - sputum; when septic - blood. Various objects of the environment (soil, water), food products, raw materials of animal origin and other material can be subjected to research. To detect the pathogen, a bacterioscopic method is used: the detection of Gram-positive rods surrounded by a capsule (in material from animals or humans) or containing spores (objects of the external environment). The main method of diagnosis - bacteriological - the isolation of pure culture and its identification, with an obligatory test for pathogenicity for laboratory animals. In cases where the test material is heavily contaminated with a concomitant, especially putrefactive, microflora, a biological test is used: subcutaneously infect white mice or guinea pigs. In the presence of B. Anthracis, mice and guinea pigs perish in 24-26 h, rabbits after 2-3 days, in cases of general sepsis; The spleen is sharply enlarged, at the place of introduction of the material - the infiltrate. In preparations-smears from blood and organs - capsule sticks.

Of the number of serological reactions with a diagnostic purpose, the reaction of Ascoli thermochemical precipitation is used in the main. It is used in cases where it is difficult to count on the isolation of the pure culture of the pathogen (in particular, in the study of wool, hides, bristles and other objects). The reaction of Ascoli is based on the discovery of thermostable antigens of the pathogen, which persist much longer than the viable vegetative cells and spores of the anthrax bacillus. For retrospective diagnosis of anthrax, an allergic test with anthraxin is used.

Anthrax Treatment

Treatment of anthrax is complex. It is aimed at neutralizing the toxin and against the pathogen: anti-STI immunoglobulin and antibiotics (penicillins, tetracyclines, erythromycin, etc.) are used.

[13], [14], [15], [16], [17], [18], [19],

Specific prophylaxis of anthrax

For the first time the vaccine against anthrax was obtained by L. Pasteur in 1881, in our country by L. S. Tsenkovsky in 1883 from weakened strains of B. Anthracis. Now in Russia, for the prevention of anthrax in humans and animals, a live spore capsuleless STI vaccine is used, which is prepared from the avirulent strain of an anthrax bacillus. The vaccine against anthrax is highly effective. Vaccinations are carried out once dermatologically or intradermally to those persons who, due to their profession, have the possibility of contracting anthrax. Revaccination is carried out after a year.