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The causative agent of melioidosis
Last reviewed: 23.04.2024
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Melioidosis - as well as sap, proceeds according to the type of severe septicopyemia in acute or chronic form with the formation of abscesses in various organs and tissues. The causative agent melioilosis was isolated and described by A. Whitmore and K. Krishnaswami in 1912.
The causative agent of melioidosis is Burkholderia pseudomallei (according to the old classification - Pseudomonas pseudomallei) - a gram-negative rod with rounded ends, 0.3-0.6 x 3-6 μm in size, is located singly or in the form of short chains. In old cultures, there are filiform, short and thick sticks, coccobacteria, etc. The spore does not form, freshly isolated bacteria often have pseudocapsules. The microbe is mobile; lofotrih, in young cultures - monotrich. Like the agent of glanders, it often gives bipolar staining, since there are polyhydroxybutyric acid inclusions located along the poles. The content of G + C in DNA is 69 mol%. A strict or facultative aerobic grows on a medium in which the only source of nitrogen is ammonium sulfate, and carbon is glucose. The optimum temperature for growth is 37 ° C, the pH of the medium is neutral. On MPA with 3-5% glycerol, glossy, smooth S-colonies grow in a day; In the future, dissociation is possible, the colonies become yellowish-brown in color, become folded. In the BCH with glycerol a uniform clouding appears every day, a sediment is formed without clearing the medium, and on the second or third day a soft film appears on the surface adjacent to the test tube wall. Then the film thickens and becomes folded. Many strains of the pathogen of melioidosis with growth on media first produce an unpleasant putrefactive odor, which then gives way to a pleasant aroma of truffles. On blood agar sometimes gives hemolysis. Fermented with the formation of acid glucose, lactose and other carbohydrates. As the culture ages, the enzymatic activity decreases. Gelatin and coagulated serum dilute. Milk peptonizes, but does not roll. Indola does not form. It has a denitrifying property and lecithinase activity.
Antigenically, the causative agent of melioidosis is quite homogeneous. He had somatic (O), shell (K), mucous (M) and flagellate (H) antigens, and somatic O-antigen is related to the O-antigen of the pathogen.
The causative agent melioidosis forms two thermolabile toxins. One of them causes hemorrhagic and necrotic lesions, the second - causes the death of laboratory animals (lethal toxin) without damaging the tissues at the injection site.
[Epidemiology of melioileosis
The source of melioilosis are rodents (rats, mice), cats, dogs, goats, sheep, pigs, cows, horses, among which epizootics can occur. In endemic areas, the pathogen is found in the soil, in the water of open water bodies contaminated by excrement of diseased animals. It is not excluded that a person can be infected not only with a contact, but also with an alimentary route. A sick person for others is not contagious. In Russia, for many decades, cases of melioidosis among people are not observed. The disease occurs in a number of countries in Southeast Asia, Europe, Africa, North and South America, Australia.
The agent melioilosis dies at a temperature of 56 ° C for 30 minutes, 1% phenol solution or 0.5% formalin solution kill it for 10 minutes. In water and soil is stored up to 1.5 months, in the corpses of animals - up to 12 days.
Symptoms of melioileosis
Infection of a person occurs predominantly through damaged skin or mucous membranes upon contact with water or soil. In which the pathogen of melioidosis is contained. The incubation period of melioilosis is from 4 days to several months. The causative agent melioilosis reproduces in the blood, spreads throughout the body, which leads to the formation of abscesses in various organs and tissues.
The course of melioileosis can be acute and chronic. The prognosis is always serious, the disease can last for months and even years.
Laboratory diagnostics of melioileosis
Bacteriological, serological and biological methods are used. To isolate a clean culture, take blood, sputum, pus from abscesses, separated from the nose and urine, and also cadaveric material. The blood of patients is sown on a glycerol BCH, any other material is taken for glycerol agar. The causative agent, unlike other pseudomonads, is resistant to polymyxin at a concentration of 400 μg / ml.
Along with the sowing of the material, guinea pigs or hamsters are infected on medium: the blood of patients is injected intraperitoneally, the other material is injected subcutaneously or by rubbing into scarified skin. With a positive result at the injection site, edema, necrosis, ulcer develops, abscesses appear in the lymph nodes. When the deceased animal is autopsied, multiple abscesses are found in the internal organs; of them, it is easy to single out a pure culture.
To detect specific antibodies in the blood of patients or those who have recovered, use RSK, RPGA and agglutination reaction. Increasing antibody titers in these reactions is an important diagnostic sign, but in this case it is not always possible to differentiate melioidosis from sapa.
Specific prevention of melioileosis
Specific prophylaxis of melioileosis has not been developed. General prophylaxis is reduced to carrying out deratization activities in areas that are not safe for melioidosis, preventing rodents from accessing water sources, dwellings and products. Prohibit bathing in stagnant water bodies, use of non-contaminated water. Sick pets are isolated, treated (or destroyed).