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Actinomycetes
Last reviewed: 23.04.2024
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Actinomycetes are branching bacteria. Do not contain chitin or cellulose in the cell wall, unlike fungi, have the structure of gram-positive bacteria. Mycelium is primitive. Thin straight or slightly curved sticks with a size of 0.2-1.0x2.5 microns, often form strands up to 10-50 microns in length.
They are able to form a well developed mycelium; in some species it is long, rarely branching; in others it is short and strongly branched, mycelium hyphae are not septate. Rod-like forms, often with angle-like ends, are arranged singly, in pairs, in the smear. V- and Y-shaped or in the form of a palisade. All morphological forms are capable of true branching, especially on a thioglycolic semi-fluid medium. Gram stain poorly, often form granular or distinct forms, conidia do not form, are not acid-fast. A typical species is Actinomyces hovis.
The cultural properties of actinomycetes
Obligatnye and facultative anaerobes, kaphnofily. Grow slowly, crops should be cultivated for 7-14 days. Temperature optimum of growth of 37 C Some strains give hemolysis on media with blood. Some species form filamentous microcolonies reminiscent of mycelium, and on the 7-14th day form crumbly S-shaped colonies, sometimes painted in yellow or red. Actinomyces israelii is inclined to form a long branching mycelium, eventually degrading into polymorphic coccoid, tubular and other elements. On simple nutrient media it grows poorly, it grows better on protein media containing serum; forms transparent colorless pasty, usually smooth colonies, densely intergrown with the environment. Aerial mycelium is lean, pigments do not form, on some media, for example on blood agar, can form white tuberous colonies, A. Odontoiyticm on blood agar forms red colonies with hemolysis zone.
Biochemical activity of actinomycetes
Actinomycetes are chemo-organotrophs. Ferment the carbohydrates with the formation of acid without gas, fermentation products - acetic, formic, lactic and succinic acid (but not ironic). The presence of catalase and the ability to reduce nitrates to nitrites are variable in different species, indole does not form. Species differentiation is based on differences in the ability to ferment carbohydrates and in some other biochemical tests.
In the ELISA, serogroups A, B, C, D, E, F are isolated.
[7], [8], [9], [10], [11], [12]
Ecological niche of actinomycetes
The main habitat is the soil. Constantly found in water, air, various objects, covers of plants, animals and humans. Colonize the mucous membrane of the mouth of man and mammals.
[13], [14], [15], [16], [17], [18]
Stability of actinomycetes in the environment
When you hit the air instantly die.
Sensitivity to antimicrobial agents. Sensitive to penicillins, tetracycline, erythromycin and clindamycin. Sensitive to the action of commonly used antiseptics and disinfectants.
Epidemiology of Actinomycosis
The source of infection is the soil. The multiplicity of mechanisms, paths and transmission factors is typical, although the transmission mechanism is the most contact, and the transmission path is wounded. Susceptibility to actin and cet, as to all conditionally pathogenic microbes, is low in individuals with normal immune status and elevated in immunodeficient hosts.
Symptoms of Actinomycosis
Actinomycosis is a chronic opportunistic infection of humans and animals caused by anaerobic and facultative anaerobic actinomycetes, which is characterized by granulomatous inflammation with polymorphic symptoms.
The disease of actinomycosis is manifested by the formation of a granuloma that undergoes a necrotic decay with the formation of pus leaving the fistula on the surface of the skin and mucous membranes of different consistency, yellowish white, sometimes with an admixture of blood, often containing druses. At the same time there is fibrosis of the granuloma. Depending on the localization, there are cervico-facial, thoracic, abdominal, genitourinary, osteoarticular, musculoskeletal, septic and other forms of the disease.
Immunity has not been studied enough.
Laboratory diagnostics of actinomycosis
The material for the study is sputum, cerebrospinal fluid, pus from fistula, punctures of unopened foci of softening, scrapings from granulations, tissue obtained from biopsy.
To diagnose actinomycosis bacterioscopic, bacteriological, serological and allergic methods are used.
Usually, the diagnosis is made by bacterioscopy on the detection of actinomycete druses in the test material, which have the appearance of small yellowish or grayish-white granules with a greenish outflow. Under a small increase, formations of a circumferential form with an unstructured center and a periphery of the radial structure are visible; under a large increase in the center visible plexus with pigmented grains, on the periphery of this coil mycelium depart radially in the form of rays of hyphae with bulbous bulges at the ends. According to Gram, spores are colored in dark purple, mycelium - in violet. According to Tsil-Nelson, the mycelium is dyed blue and the spores are red.
The final diagnosis is established on the basis of excretory excretion. To suppress the growth of concomitant microflora, pus and sputum before centrifuge are centrifuged in a solution of penicillin and streptomycin, then washed with an isotonic NaCl solution to remove antibiotics. They are inoculated on nutrient media (sugar agar, Saburo medium, etc.) and cultivated under aerobic and anaerobic conditions. Isolate and identify the pure culture according to the generally accepted scheme. The isolated cultures are determined by the ability to fold and peptonize milk - a characteristic characteristic of actinomycetes. Isolation of anaerobic species confirms the diagnosis of actinomycosis.
For the serodiagnosis of actinomycosis, RAC is placed with actinolysate. The reaction is not specific enough, since positive results can be noted in lung cancer and heavy suppuration. Application as an antigen instead of actinolysate extracellular proteins of actinomycetes increases the sensitivity of DSC. The same antigen can also be used for the formulation of RNGA.
The allergic test is carried out with actinolysate. Diagnostic value is only positive and sharply positive samples. With visceral actin and goat, the allergic test is often negative.