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Pseudomonas aeruginosa
Last reviewed: 22.11.2021
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The genus Pseudomonas belongs to the family Pseudomonadaceae (class Gammaproteobacteria, type Proteobacteria) and contains more than 20 species. Some of them are natural inhabitants of soil and water and therefore play a huge role in the circulation of substances in nature. Other species play a significant role in human pathology (see also "Pathogens of sapa and melioidosis "), animals and plants.
Pseudomonas are gram-negative non-fermenting bacteria, which include representatives of the genus Pseudomonas, a type species - Pseudomonas aeruginosa (Pseudomonas aeruginosa), which is the causative agent of many pyoinflammatory diseases, as well as some other species. Pseudomonas aeruginosa (bluelegon bacillus)
The name of the bacteria was obtained for the characteristic blue-green staining of the purulent discharge, which was first described by A. Lyuke in 1862. However, in pure culture, the causative agent was isolated by S. Jessar only in 1 82. P. Aeruginosa belongs to the family Pseudomonadaceae.
Biochemical properties of Pseudomonas aeruginosa
Pseudomonads are Gram-negative mobile straight rods of 1-3 μm in size, located singly, in pairs or in the form of short chains. The mobility of Pseudomonas aeruginosa is provided by the presence of one, rarely two polarly located flagella (mopotriha or amphitrichi). Dispute does not form, they have saws of type IV (pili). Under certain conditions, they can produce capsular-like extracellular mucus of polysaccharide nature. There are also so-called mucoid strains, which form an increased amount of mucus. Such bacteria are most often isolated from sputum from patients with cystic fibrosis.
All pseudomonads are obligate aerobes that grow well on simple nutrient media. On a liquid nutrient medium, bacteria form a characteristic grayish-silvery film on the surface. On the blood agar around the colonies of the pseudomonas a hemolysis zone is observed, selective or differential diagnostic nutrient media with the addition of antiseptics - malachite agar with the addition of brilliant green or CPC-agar with acetamide - are used to isolate the pure culture of Pseudomonas aeruginosa. The optimum growth temperature is 37 ° С, however, the Pseudomonas aeruginosa is able to grow at 42 ° C, which makes it possible to distinguish it from other pseudomonads. Colonies of Pseudomonas aeruginosa smooth rounded, dry or mucous (in capsular strains). When cultivated on dense nutrient media P. Aeruginosa produces a peculiar sweetish smell of jasmine, strawberry soap or caramel. A characteristic biological feature of P. Aeruginosa bacteria is also their ability to synthesize water-soluble pigments that color the patient's dressings or nutrient media during their cultivation. Most often they produce a phenazine pigment-a pyocyanin of a blue-green color, but can also form a green fluorescent in UV - Pigment fluorescein (pyoverdin), as well as red (pirubin), black (piomelanin) or yellow (oxyphenazine).
Pseudomonas aeruginosa does not ferment glucose and other carbohydrates, but it can oxidize to produce energy. For differential diagnosis, which makes it possible to distinguish pseudomonads from other gram-negative bacilli, an OF test (glucose oxidation / fermentation test) is used on a special medium. For this, a pure culture of pseudomonads is inoculated into two test tubes, one of which is then incubated under aerobic conditions and the other in anaerobic. Pseudomonads are only able to oxidize lactose, so the color of the indicator only changes in a test tube that is aged under aerobic conditions. P. Aeruginosa restores nitrates to nitrites, and also has proteolytic activity: liquefies gelatin, hydrolyses casein. Pseudomonas aeruginosa has catalase and cytochrome oxidase.
Many strains of Pseudomonas aeruginosa produce bacteriocins, called piozines, which have bactericidal properties. Piocinotyping of Pseudomonas aeruginosa strains is used for epidemiological marking and intraspecific identification of P. Aeruginosa. To this end, determine the spectrum of piocins released by the strain under study, or its sensitivity to the piocins of other pseudomonads.
[10], [11], [12], [13], [14], [15], [16], [17], [18], [19], [20]
Antigenic properties of Pseudomonas aeruginosa
Pseudomonas aeruginosa has a complex antigenic structure, due to the presence of O and H antigens. LPS of the cell wall is a type-specific thermostable O-antigen and is used for serotyping P. Aeruginosa strains. Thermolabile flagellate H-antigen is protective, and on its basis vaccines are obtained. On the surface of the cells of the Pseudomonas aeruginum, antigens of pili (fimbriae) were also found. In addition, P. Aeruginosa produces a number of extracellular products with antigenic properties: exotoxin A, protease, elastase, extracellular mucus.
Factors of pathogenicity of Pseudomonas aeruginosa
One of the main factors of pathogenicity of Pseudomonas aeruginosa and other pseudomonads is O-antigen-lipopolysaccharide of the cell wall, the mechanism of action of which is the same as in other gram - negative bacteria.
P. Aeruginosa has a variety of pathogenicity factors that are involved in the development of Pseudomonas aeruginosa infection. Among the most important of them distinguish the following.
Adhesion and colonization factors - sawed type iV (pili) and extracellular (extracellular mucus) P. Aeruginosa.
[26], [27], [28], [29], [30], [31], [32], [33], [34]
Toxins
LPS of the outer membrane of the cell wall P. Aeruginosa has the properties of endotoxin and is involved in the development of fever, oliguria, and leukopenia in patients.
Exotoxin A of Pseudomonas aeruginosa is a pitotoxin that causes profound disturbances of cellular metabolism as a result of suppression of protein synthesis in cells and tissues. Like the diphtheria toxin, it is an ADP-ribosyltransferase that inhibits the EF-2 elongation factor and therefore causes a disruption in protein synthesis. It has also been shown that exotoxin A, along with the protease, suppresses the synthesis of immunoglobulins and causes neutropenia. Exotoxin A is produced in an inactive form in the form of protoxin and is activated with the participation of various enzymes within the body. Exotoxin A has protective properties, ie antibodies to it protect the host cells from its damaging effect, and also prevent the development of bacteremia and Pseudomonas septicemia.
Exotoxin S (exotzyme S) is found only in highly virulent strains of Pseudomonas aeruginosa. The mechanism of its damaging effect on cells is not yet clear, but it is known that infections caused by exoenzyme-3-producing strains of Pseudomonas aeruginosa often terminate lethal. Exotoxins A and S also interfere with the activity of phagocytes.
Leucocidin is also a cytotoxin with a pronounced toxic effect on human granulocytes.
Enterotokin and permeability factors play a role and development of local tissue lesions in intestinal forms of Pseudomonas aeruginosa, causing disturbances in water-salt metabolism.
Enzymes of aggression
P. Aeruginosa produces hemolysins of two types: thermolabile phospholipase C and thermostable glycolipid. Phospholipase C destroys phospholipids in the composition of surfactants on the alveolar surface of the lungs, causing the development of atelectasis (bronchiectasis) in the pathology of the respiratory tract.
Neuraminidase also plays an important role in the pathogenesis of broncho-pulmonary diseases of Pseudomonas etiology and cystic fibrosis, as it participates in the colonization of mucin in the respiratory tract.
Elastase, as well as other proteolytic enzymes of Pseudomonas aeruginosa and exotoxin A, cause hemorrhages (hemorrhages), destruction of tissues and necrosis in lesions in eyes, pneumonia, septicemia of Pseudomonas etiology.
[35], [36], [37], [38], [39], [40], [41], [42]
Pseudomonad resistance
P. Aeruginosa is characterized by a rather high resistance to antibiotics, which is due to the poor permeability of the outer membrane of these bacteria due to a congenital defect of porins, and the ability of bacteria to synthesize penicillinase.
P. Aeruginosa maintains viability in conditions of almost complete absence of food sources: it is well preserved in fresh, marine and even distilled water. It is also proved that Pseudomonas cultures can be preserved and even multiply in solutions of disinfectants (for example, furicillin) intended for storing catheters and various medical instruments, washing wounds in burn and surgical hospitals.
At the same time, P. Aeruginosa is sensitive to drying, the action of chlorine-containing disinfectants and is easily inactivated when exposed to high temperatures (boiling, autoclaving).
Epidemiology of diseases caused by Pseudomonas aeruginosa
The disease of Pseudomonas aeruginosa can develop as a result of autoinfection (endogenous infection) or exogenously. The source of infection are people (sick or bacterial carriers), as well as various natural reservoirs of nature (soil and various fresh and salt water bodies). It has been established that about 5-10% of healthy people are carriers of various strains of P. Aeruginosa (they normally colonize the intestine) and about 70% of patients in the hospital. Pseudomonas are also found everywhere: in water and ventilation systems, fruits and vegetables, houseplants, on the surface of soap, for hand washing, towels, breathing apparatus, etc. Therefore, Pseudomonas aeruginosa infection can be considered saproanthroponosis. Mechanisms and ways of infection in infections caused by Pseudomonas aeruginosa are contact, respiratory, blood, fecal-oral.
Pseudomonasplastic infection can occur in immunodeficient individuals with severe concomitant pathology (diabetes, burn disease, leukemia, cystic fibrosis, immunosuppression in cancer and organ transplantation), and at the foyer of normal immunological reactivity of the body. It is known that the adhesive activity of P. Aeruginosa increases with increasing ambient temperature, so visiting the pool, baths, taking medicinal baths can also provoke a pseudomonas aeruginosa infection.
Pseudomonas aeruginosa is the causative agent of nosocomial (hospital) infections, i.e. Diseases that occur in people undergoing treatment in a hospital. Infection with Pseudomonas aeruginosa infection in the clinic can be associated with medical manipulations (bladder catheterization, endoscopy, wound washing, dressing, antiseptic treatment of burns, use of an artificial lung ventilation device, etc.), when infection occurs through the dirty hands of personnel, tools, on the surface of which the microbial forms a biofilm, or with the use of contaminated solutions.
Pseudomonas aeruginosa usually penetrate the human body through damaged tissues. Attaching, they populate the wound or burn surface, mucous membranes or human skin and multiply. In the absence of human immune mechanisms against Pseudomonas infection, the local process (infection of the urine of the leading tracts, skin, respiratory tract) can become common (generalized). Bacteremia leads to the spread of the pathogen and the development of sepsis, often causing the formation of secondary purulent foci of infection. Under the influence of pathogenicity factors (exotoxins, enzymes of aggression), there is a disruption in the functioning of organs and systems and severe complications can develop - the syndrome of disseminated intravascular coagulation, shock, and respiratory distress syndrome.
Symptoms of diseases caused by Pseudomonas aeruginosa
Pseudomonas aeruginosa causes purulent-inflammatory diseases of various locations: wound infections, burn disease, meningitis, urinary tract infections, skin, eye diseases, necrotic pneumonia, sepsis, etc. Mortality from Pseudomonas septicemia reaches 50%.
Immunity
Antiparasitic and antibacterial antibodies are found in the blood serum of healthy people, as well as those with Pseudomonas aeruginosa infection, but their role in protection against recurrent diseases has been little studied.
Laboratory diagnosis of diseases caused by Pseudomonas aeruginosa
The main method of diagnosis is a bacteriological study. Materials for the study are blood (with septicemia), spinal fluid (with meningitis), pus and wound discharge (with infected wounds and burn lesions), urine (with infections of the urinary tract), sputum (for infections of the respiratory tract), etc. Bacterioscopy of smears from the studied material is little informative. When identifying P. Aeruginosa, the nature of their growth on CPC agar, the pigmentation, the presence of a characteristic specific culture odor, the positive pitochromoxidase test, the detection of thermophilicity (growth at 42 ° C), the ability to oxidize glucose in the OF test are taken into account. For intraspecific identification of bacteria, serotyping, pyopinotyping, phagotyping are carried out.
The serological test method is aimed at the detection of specific antibodies to Pseudomonas aerugin (usually exotoxin A and LPS) with the help of RSK, RPGA opsono-phagocytic reaction and some other tests.
Treatment of diseases caused by Pseudomonas aeruginosa
For the treatment of Pseudomonas aeruginosa, antibiotics are used, combining drugs from different groups is recommended. Antimicrobial therapy is prescribed only after determining the antibioticogram. In emergency cases, antibiotics are used empirically.
To treat severe forms of Pseudomonas aeruginosa infection, hyperimmune plasma obtained from the blood of volunteers immunized with polyvalent corpuscular synaptic vaccine is also used.
Local treatment of skin infections (trophic ulcers, ecstema, burn wounds) caused by P. Aeruginosa, use antisignogenic heterologous immunoglobulin, obtained from the serum of rams, hyperimupted by suspension of cultures of Pseudomonas aeruginosa of 7 different immunotypes killed by formalin.
In addition, for the treatment of purulent infections of the skin, abscesses, thermal burns complicated by Pseudomonas aeruginosa, cystitis, mastitis and other diseases of Pseudomonas aeruginosa (except for sepsis), you can use a pseudomonas bacteriophage (bacteriophage pioceansus) or polyvalent liquid pyobacteriophage.
Prophylaxis of diseases caused by Pseudomonas aeruginosa
Effective sterilization, disinfection and antiseptics, as well as compliance with asepsis rules are the main measures of non-specific prevention of Pseudomonas aeruginosa infection in the hospital. The plan of preventive measures must necessarily include control over the contamination of the environment (air, various objects, tools and equipment), observance of personal hygiene rules.
For the purpose of non-specific prophylaxis of purulent-inflammatory diseases, it is recommended that patients with weakened anti-infectious immunity be prescribed immunomodulators.
To create active immunity against Pseudomonas infection vaccines are used. Currently, vaccines have been developed from LPS Pseudomonas aeruginosa, polysaccharide subcorpuscular (chemical) vaccines, ribosomal vaccines, preparations from flagellum antigens P. Aeruginosa and extracellular mucus components, as well as toxins from extracellular proteases and exotoxin A. In Russia, a polyvalent corpuscular synaptic vaccine from 7 strains of P. Aeruginosa) and staphyloprotein-Pseudomonas aeruginosa vaccine.
Active immunization against infections caused by P. Aeruginosa is indicated for patients at risk (patients with cystic fibrosis, diabetes, and immunodeficient individuals). However, due to the fact that the immune response to vaccine preparations in people with immunodeficiency is late and not always full. Great importance is attached to combining methods of active and passive immunization.