Legionella

Currently, more than 50 species of legionella are known, in the human pathology the role of 22 species has been shown so far. 95% of cases are due to the type of L. Pneumophila, which is typical. Its name is associated with the first victims of the disease caused by him among the participants of the Congress "American Legion", held in Philadelphia in the summer of 1976. In 1977, the causative agent was isolated from the lungs of the victims D. McDead and S. Shapard.

[1], [2], [3], [4], [5], [6], [7],

The cultural properties of legionella

Aerobics. These bacteria multiply only on complex nutrient media (buffer-coal yeast agar) with the mandatory addition of cysteine, iron pyrophosphate and ketoglutaric acid in connection with the requirements for these substances. Cultivation is carried out at 35 ° C in an atmosphere of 2.5-3% CO; for 3-6 days. The colonies grown on the nutrient medium have an ingrown center with the formation of a brown pigment, except for the species L. Micdadei. Can be cultured in the yolk sac of the chick embryo and cell cultures in the guinea pig body.

Biochemical properties of legionella

Catalase-positive. Do not ferment carbohydrates, do not produce urease, do not restore nitrates. Some species dilute gelatin. L. Pneumophila from other species of legionella is characterized by its ability to hydrolyze sodium hypprurate.

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

Antigenic structure of legionella

Complex. The species of L. Pneumophila is divided into 16 serogroups, the specificity of which is mediated by a lipopolysaccharide antigen.

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

Resistance of Legionella

Like other spore-forming bacteria, they are sensitive to UV rays, ethyl alcohol, phenol, 3% chloramine solution.

Pathogenicity factors of legionella

Legionella are facultative intracellular parasites. In the human body, they multiply primarily in the alveolar macrophages into which they fall due to inhalation of microbial aerosols, as well as in polymorphonuclear and monocytes of blood. Legionella actively multiply in macrophages, which leads to the destruction of the latter and the release of a large number of bacteria into the lung tissue. This process is provided by the following factors of pathogenicity: cytotoxin and superoxide dismutase, suppressing the respiratory explosion of the phagocyte; cytolysin, which is an enzyme metalloprotease preventing the formation of phagolysosomes, as well as causing hemorrhagic effect: the death of bacteria released endotoxin, causing intoxication.

The repeatedly repeated cycle of interaction of legionella with macrophages of the lungs leads to the accumulation of the pathogen in a high concentration and the development of an acute inflammatory process.

Immunity

Immunity cellular. Antibodies have no protective activity.

Epidemiology of legionellosis

In natural conditions legionella live in freshwater reservoirs, where they are symbionts of algae, water and soil amoebae and other protozoa. The high adaptive capabilities of legionella allow them to successfully colonize artificial reservoirs, water supply and air conditioning systems, and medical equipment. On synthetic and rubber surfaces of water, industrial and medical equipment, legionella form biofilm, in which they become more resistant to the action of disinfectants.

Mechanism of transmission of legionellosis infection aspiration. The main transmission factor is a fine aerosol containing legionella formed by domestic, medical or industrial water systems. From person to person, the disease will not be transmitted. The disease is widespread. Including in Russia. The peak incidence falls on the summer months. The predisposing factor is the immunodeficiency state.

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

Symptoms of legionellosis

Three clinical forms of legionellosis are known: Legionnaires' disease (Philadelphia fever) and Pontiac fever, Fort Bragg fever.

The incubation period of Legionnaires' disease is 2-10 days. The disease is accompanied by fever, chills, pain in the chest, shortness of breath. In 20-30% of cases, acute respiratory failure develops. Infectious-toxic shock, renal insufficiency, and damage to the central nervous system can develop. Mortality is 8-25%, in patients with immunodeficiency 60%.

Pontiac fever is an acute respiratory disease without pneumonia. The incubation period is 36-48 hours. The disease is characterized by a 1-2-day fever, catarrhal phenomena in the nasopharynx, dry cough. Lethal outcomes are not recorded. The disease affects 95-100% of persons in the aerosol distribution zone.

Fort-Brag fever is an acute febrile illness with exanthema. The risk of nosocomial legionellosis is associated with the possibility of contamination of legionella: water supply systems, air conditioning and medical equipment, as well as the presence of persons susceptible to infection, with violation of cellular immunity. In addition to L. Pneumophila, the nosocomial infection of the lower respiratory tract is caused by L. Micdadei.

Diagnosis of legionellosis

Laboratory diagnostics of legionellosis is carried out by bacteriological, serological and express methods.

The material for the isolation of legionella is sputum, bronchoscopy material, pleural exudate, biopsy material of the lungs, which is stored for no more than 1 day at 4 ° C.

Serological examination is performed by determining the 4-fold increase in antibody titre in paired sera by ELISA or indirect RIF.

Also, a determination is made on the 2-10th day of the soluble antigen in the urine using an ELISA or an immunochromatographic method.

Direct RIF and PCR is used as an express diagnostic. However, a specific reliable result is obtained only if the materials for the study are bronchoscopy materials and biopsies, and not sputum.

[24], [25], [26], [27],

Treatment of legionellosis

Treatment of legionellosis consists in the appointment of antibiotics, capable of intracellular penetration: macrolides (erythromycin, clarithromycin, azithromycin) and fluorolinolones.

Prevention of legionellosis

Legionellosis can not be prevented with the help of specific prevention methods. Nonspecific prophylaxis of legionellosis is reduced to periodic cleaning of water systems, revealing the water reservoir of the pathogen and its recovery.