Bordetelles

Pertussis is an acute infectious disease of mainly childhood, characterized by a cyclic course and paroxysmal spasmodic cough.

The causative agent - Bordetella pertussis - was first detected in 1900 in smears from the sputum of a child and then isolated in pure culture in 1906 by J. Borde and O. Zhang. The causative agent similar to whooping cough, but more easily transmitted disease - bordetella parapertussis - was isolated and studied in 1937 by G. Eldering and P. Kendrick and independently by them in 1937 by W. Bradford and B. Slavin. Bordetella bronchiseptica, the causative agent of a rarely pertussis-like disease in humans, was isolated in 1911 in dogs by N. Ferri, and in man in 1926 by Brown. In 1984, a new species was identified - Bordetella avium, the pathogenicity of which has not yet been established for humans.

[1], [2], [3], [4]

Bordetell morphology

Bordetella belong to the class of Betaproteobacteria, gram-negative, well colored with all aniline dyes. Sometimes bipolar coloration is detected due to the volute grains at the poles of the cell. The pertussis causative agent has the form of an ovoid bacillus (coccobacterium) 0.2-0.5 x 1.0-1.2 μm in size. Paracoid bacillus has the same shape, but somewhat larger (0.6 x 2 μm). Are located more often singly, but can be located in pairs. Dispute does not form, in young cultures and in bacteria isolated from the macroorganism, a capsule is found. Bordetella motionless, with the exception of B. Bronchiseptica, which is a peritrich. The content of G + C in DNA is 61-70 mole%. Relate to hemophilic bacteria.

[5], [6], [7], [8], [9]

Biochemical properties of Bordetella

Bordetelles - strict aerobes, chemo-organotrophs. The optimum growth temperature is 35-36 ° C. The causative agent of pertussis in smooth S-form (the so-called phase I), unlike the other two species of Bordetella, does not grow on MPB and MPA, as its accumulation is hampered by the accumulation in the medium of unsaturated fatty acids formed during growth, the growth of colloidal sulfur and other metabolic products. To neutralize (or adsorb) them into the growth medium of pertussis bacteria, starch, albumin and charcoal or ion exchange resins should be added. The microbe requires the presence of 3 amino acids in the growth medium - proline, cysteine and glutamic acid, which are the source of hydrolysates of casein or beans. The traditional environment for the cultivation of pertussis is Borde-Gangu (potato-glycerin agar with the addition of blood), on it it grows in the form of smooth, shiny, transparent domes with a pearl or metallic mercury shade of colonies about 1 mm in diameter, 4 th day. On another medium, casein-agar agar (AMA), smooth smooth colonies with a diameter of about 1 mm, with a creamy-gray color and a viscous consistency, also grow on the third or fourth day. Colonies of paracutaneous bacteria do not differ in appearance from pertussis, but larger and are detected on the 2nd-3rd day, and colonies of B. Bronchiseptica are detected already on the 1-2-day.

A characteristic feature of pertussis bacteria is their tendency to a rapid change in cultural and serological properties when changing the composition of the nutrient medium, temperature and other growing conditions. During the transition from the S-form (phase I) to the stable rough R-form (phase IV) through the intermediate phases II and III, smooth changes in antigenic properties are observed; pathogenic properties are lost.

Paracid bacteria and B. Bronchiseptica, as well as phases II, III and IV of pertussis bacteria grow on MPA and BCH. When grown on a liquid medium, diffuse haze is observed with bottom deep sediment; cells can be somewhat larger and polymorphic, sometimes form filaments. In the R-form and intermediate forms, the bacteria show a pronounced polymorphism.

On the Borde-Gangu environment, all the bordetelles form a loosely bound hemolysis zone around the colonies, which diffuses diffusely into the medium.

Bordetelles do not ferment carbohydrates, do not form indole, do not reduce nitrates to nitrites (with the exception of B. Bronchiseptica). Paracoccus bacteria secretes tyrosinase, forming a pigment, coloring medium and culture in brown color.

Bordetella contain several antigenic complexes. Somatic O-antigen is species-specific; the generic antigen is agglutinogen. The main agglutinogens in the causative agent of whooping cough are the 7th (generic), the 1st (species) and the most commonly found type-specific 2 nd and 3 rd. Depending on their combination, Bordetella pertussis is distinguished by four serovariants: 1,2,3; 1, 2.0; 1, 0, 3, and 1.0.0.

[10], [11]

Factors of pathogenicity of Bordetella

Fimbria (agglutinogens), percutin outer membrane protein (69 kD) and filamentous hemagglutinin (surface protein) are responsible for the adhesion of the pathogen to the ciliary epithelium of the middle parts of the respiratory tract (trachea, bronchus). The capsule protects against phagocytosis. Hyaluronidase, lecithinase, plasmacoagulase, adenylate cyclase are often present. In the endotoxin (LPS) two lipids: A and X. Biological activity of LPS is determined by lipid X, lipid A has a low pyrogenicity and is non-toxic. LPS has immunogenicity (whole cell vaccine), but causes sensitization. There are three exotoxins. Pertussis toxin (117 kDa) is similar in structure and function to the cholerogen, shows the activity of ADP-ribosyltransferase (ribosylates the transducin-protein membrane of the target cell, which is part of the system that inhibits cell adenylate cyclase), a strong immunogen, increases lymphocytosis and insulin production. The tracheal cytotoxin is a fragment of peptidoglycan, has pyrogenicity, arthritogenicity, induces slow wave sleep and stimulates production of IL-1, in response to which nitric oxide is synthesized (cytotoxic factor). It damages the epithelial cells of the trachea and causes ciliostasis. The thermolabile dermonecrotoxin possesses neurotropic, vasoconstrictive activity, is homologous to the cytotoxic necrotizing factor 1 (CNF1) of Escherichia coli. Its target are the Rho-protein membrane cells. Detect dermonecrotoxin intradermal breakdown on rabbits (Dold's test).

Immunity

After the transferred disease, a stable lifelong immunity is formed; Post vaccination immunity persists only 3-5 years.

[12], [13], [14], [15], [16], [17]

Epidemiology of pertussis

The source of infection in whooping cough and paracottus is a patient with a typical or worn-out form, especially in the period before the appearance of a spasmodic cough. In pertussis-like disease caused by B. Bronchiseptica, domestic and wild animals can be the source of the infection, among which there are occasional epizootics (pigs, rabbits, dogs, cats, rats, guinea pigs, monkeys), most often the respiratory tract is affected. The mechanism of infection is airborne. Bordetelles have a specific tropism to the ciliary epithelium of the respiratory tract of the host. People of all ages are susceptible to infection, but most of all children from 1 to 10 years old.

[18], [19], [20], [21], [22], [23], [24],

Symptoms of whooping cough

The incubation period for whooping cough is from 3 to 14 days, usually 5-8 days. The causative agent, caught on the mucous membrane of the upper respiratory tract, multiplies in the cells of the ciliary epithelium and then spreads bronchogenic to the lower parts (bronchioles, alveoli, small bronchi). Under the action of exotoxin, the epithelium of the mucous membrane is necrotic, which irritates the cough receptors and creates a constant flow of signals into the cough center of the medulla oblongata, in which a stable focus of excitation is formed. This leads to spasmodic coughing attacks. Pertussis is not accompanied by bacteremia. Secondary bacterial flora can lead to complications.

During the course of the disease, the following stages are distinguished:

• catarrhal period lasting about 2 weeks. And accompanied by a dry cough; the patient's condition gradually worsens;
• convulsive (convulsive), or spasmodic, a period lasting up to 4-6 weeks. And characterized by bouts of indomitable barking cough that occur up to 20-30 times a day, and attacks can be provoked even by nonspecific stimuli (light, sound, smell, medical manipulation, examination, etc.);
• the period of resolution, when coughing attacks become less frequent and less and more prolonged, necrotic areas of the mucous membrane of the upper respiratory tract, often in the form of "casts" from the trachea and bronchi, are rejected; duration - 2-4 weeks.

Laboratory diagnosis of pertussis

The main diagnostic methods are bacteriological and serological; for accelerated diagnosis, especially at an early stage of the disease, the immunofluorescence reaction can be used. To isolate a pure culture, mucus from the nasopharynx or sputum is used as the material, which is sown on an AMC or Borde-Zhang environment. Sowing can also be done by the method of "cough plates". The grown culture is identified by a combination of cultural, biochemical and antigenic properties. Serological reactions - agglutination, complement fixation, passive hemagglutination - are put mainly for the retrospective diagnosis of pertussis or in cases where a pure culture is not isolated. Antibodies to the pathogen appear no earlier than the 3rd week. Disease, the diagnosis is confirmed by an increase in antibody titer in sera taken with a 1-2-week interval. In children of the first two years of life, serological reactions are often negative.

Treatment of pertussis

For treatment, antibiotics (gentamicin, ampicillin), effective in catarrhal and useless in convulsive period, are used.

Specific prophylaxis of pertussis

For routine prophylaxis of the disease, children are vaccinated against whooping cough, use adsorbed pertussis-diphtheria-tetanus vaccine (DTP), containing 20 billion killed pertussis bacteria in 1 ml. The same component is based on the separately manufactured pertussis vaccine, which is used in children's groups for epidemiological indications. This component is reactogenous (neurotoxic property), so now acellular vaccines containing from 2 to 5 components (pertussis anatoxin, filamentous hemagglutinin, pertactin and 2 agglutinogen of fimbriae) are actively studied.