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Staphylococci

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Last reviewed: 01.06.2018
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Staphylococcus was discovered in 1878 by R. Koch and in 1880 by L. Pasteur in a purulent material. L. Pasteur, after infecting a rabbit, finally proved the role of staphylococcus as a pathogen of purulent inflammation. The name "staphylococcus" was given in 1881 by A. Ogston (because of the characteristic arrangement of the cells), and described in detail its properties in 1884 by F. Rosenbach.

Staphylococci are gram-positive, regular geometric forms of spherical cells 0.5-1.5 microns in diameter, usually located in the form of clusters, catalase positive, reduce nitrates to nitrites, actively hydrolyse proteins and fats, ferment in anaerobic conditions glucose to form an acid without gas. Usually can grow in the presence of 15% NaCl and at a temperature of 45 ° C. The content of G + C in DNA is 30-39 mol%. Staphylococci do not have flagella, do not form a dispute. They are widespread in nature. Their main reservoir is the skin of humans and animals and their mucous membranes, communicating with the external environment. Staphylococci are facultative anaerobes, only one species (Staphylococcus saccharolyticus) is a strict anaerobic. Staphylococci are not exacting to nutrient media, they grow well on ordinary media, the temperature optimum for growth is 35-37 "C, pH 6.2-8.4 Colonies are round, 2-4 mm in diameter, with even edges, convex, opaque, are colored in the color of the pigment formed.The growth in liquid culture is accompanied by Uniform cloudiness, with time a loose sediment precipitates.Without growth on ordinary media, staphylococci do not form capsules, however, when sown to a semisolid agar with plasma or serum, most strains of S. Aureus form a capsule. Strains in luzhid agar grow in the form of compact colonies, capsular - form diffuse colonies.

Staphylococci have a high biochemical activity: they ferment with the release of acid (without gas), glycerin, glucose, maltose, lactose, sucrose, mannitol; form various enzymes (plasmacoagulase, fibrinolysin, lecithinase, lysozyme, alkaline phosphatase, DNase, hyaluronidase, tellurite reductase, proteinase, gelatinase, etc.). These enzymes play an important role in the metabolism of staphylococci and largely determine their pathogenicity. Such enzymes, as fibrinolysin and hyaluronidase, cause high invasiveness of staphylococci. Plasmacoagulase is the main factor of their pathogenicity: it protects against phagocytosis and converts prothrombin to thrombin, which causes clotting of fibrinogen, as a result of which each cell is covered with a protein film that protects against phagocytes.

trusted-source[1], [2], [3], [4], [5], [6], [7]

Factors of pathogenicity of staphylococci

Staphylococcus is a unique microorganism. It can cause more than 100 different diseases related to eleven classes according to the International Classification of 1968. Staphylococci can affect any tissue, any organ. This property of staphylococci is due to the presence of a large complex of pathogenicity factors.

Adhesion factors - the attachment of staphylococci to tissue cells is due to their hydrophobicity (the higher it is, the more pronounced adhesive properties), as well as the adhesive properties of polysaccharides, possibly also protein A, and the ability to bind fibronectin (the receptor of some cells).

Various enzymes that play the role of "aggression and protection" factors: plasmacoagulase (the main pathogenicity factor), hyaluronidase, fibrinolysin, DNase, lysozyme-like enzyme, lecithinase, phosphatase, proteinase, etc.

Complex of secreted exotoxins:

  • membrane-damaging toxins - a, p, 8 and y. Previously, they were described as hemolysins, necroxins, leukocidins, lethal toxins, ie, by the nature of their action: hemolysis of erythrocytes, necrosis with intradermal administration of a rabbit, destruction of leukocytes, death of a rabbit with intravenous administration. However, it turned out that this effect is caused by the same factor - membrane-damaging toxin. It has a cytolytic effect on various types of cells, which manifests itself as follows. The molecules of this toxin first bind to the currently unknown receptors of the target cell membrane or are absorbed non-specifically by the lipids contained in the membrane, and then a 7-molecule fungal heptamer consisting of 3 domains is formed. The domains forming the "hat" and the "edge" are located on the outer surface of the membranes, and the "foot" domain serves as a transmembrane channel-at times. Through it, small molecules and ions enter and exit, leading to the swelling and death of cells that have a nucleus and the osmotic lysis of red blood cells. Several types of membrane-damaging (pore-forming) toxins have been detected: a-, b-, s- and y-hemolysins (a-, b-, S- and y-toxins). They differ in a number of properties. Hemolysin is more often found in staphylococci isolated from a person, it lyses the red blood cells of humans, rabbits and rams. Lethal effect in rabbits is caused by intravenous administration in 3-5 minutes. Hemolysin b is found more often in staphylococci of animal origin, it lyses human and lamb erythrocytes (preferably at a lower temperature). Hemolysin S lysates the erythrocytes of humans and many animal species. Lethal effect on the rabbit with intravenous administration causes in 16-24-48 hours Very often in staphylococci are found a- and 8-toxins at the same time;
  • exfoliative toxins A and B are distinguished by their antigenic properties, the ratio to temperature (A is thermostable, B is thermolabile), the localization of genes controlling their synthesis (A is controlled by a chromosomal gene, B is plasmidic). Often, both exfoliatin are synthesized from the same strain of S. Aureus. These toxins are associated with the ability of staphylococci to cause pemphigus in newborns, bullous impetigo, scarlet fever-like rash;
  • true leukocidin, a toxin that differs from hemolysins by antigenic properties, selectively acts on leukocytes, destroying them;
  • Exotoxin, which causes toxic shock syndrome (STS). It has the properties of superantigen. STS is characterized by an increase in temperature, a decrease in blood pressure, skin rashes followed by desquamation on hands and feet, lymphocytopenia, sometimes diarrhea, kidney damage, etc. More than 50% of strains of S. Aureus are capable of producing and secreting this toxin.

Strong allergenic properties, which possess both components of the cell structure, and exotoxins and other secreted by bacteria products of vital activity. Staphylococcal allergens can cause hypersensitivity reactions of both delayed type (GCHZ) and immediate type (GCHN) - Staphylococcus are the main culprits of skin and respiratory allergies (dermatitis, bronchial asthma, etc.). The peculiarity of the pathogenesis of staphylococcal infection and its tendency to transition to a chronic form are rooted in the effect of GCHZ.

Cross-reacting antigens (with erythrocyte isoantigens A and B, kidney and skin - induction of autoantibodies, development of autoimmune diseases).

Factors that inhibit phagocytosis. Their presence can be manifested in inhibition of chemotaxis, protection of cells from absorption by phagocytes, in ensuring the ability of staphylococci to multiply in phagocytes and blocking the "oxidative explosion". Phagocytosis inhibits the capsule, protein A, peptidoglycan, teichoic acids, toxins. In addition, staphylococci induce the synthesis of suppressors of phagocytic activity by certain cells of the body (for example, splenocytes). The inhibition of phagocytosis not only prevents the purification of the body from staphylococci, but also disrupts the function of processing and representing antigens to T and B lymphocytes, which leads to a decrease in the strength of the immune response.

The presence of a capsule in staphylococci increases their virulence for white mice, makes them resistant to phages, does not allow typing with agglutinating sera and masks protein A.

Teichoic acids not only protect staphylococci from phagocytosis, but, obviously, play an important role in the pathogenesis of staphylococcal infections. It was found that in children with endocarditis, antibodies to teichoic acids are detected in 100% of cases.

Mitogenic action of staphylococci against lymphocytes (protein A, enterotoxins and other products secreted by staphylococci possess this action).

Enterotoxins A, B, CI, C2, C3, D, E. They are characterized by antigenic specificity, thermostability, resistance to formalin (do not turn into toxoids) and digestive enzymes (trypsin and pepsin), are stable in the pH range from 4.5 to 10.0. Enterotoxins are low-molecular proteins with a mass of 26 to 34 kD with the properties of superantigens.

It is also established that there are genetically determined differences in the sensitivity to staphylococcal infection and the nature of its course in humans. In particular, severe staphylococcal purulent-septic diseases are more often found in people with blood groups A and AB, less often in individuals 0 and B groups.

With the synthesis of enterotoxins, the ability of staphylococci to cause food poisoning such as intoxication is associated. Most often they are caused by enterotoxins A and D. The mechanism of action of these enterotoxins has been little studied, but it differs from the action of other bacterial enterotoxins that disrupt the function of the adenylate cyclase system. All types of staphylococcal enterotoxins cause a similar pattern of poisoning: nausea, vomiting, pancreatic pain, diarrhea, sometimes headache, fever, muscle spasm. These features of staphylococcal enterotoxins are due to their superantigenic properties: they induce excessive synthesis of interleukin-2, which causes intoxication. Enterotoxins excite the smooth muscles of the intestine and increase the motility of the gastrointestinal tract. Poisoning is most often associated with the use of dairy products infected with staphylococcus (ice cream, cakes, cakes, cheese, cottage cheese, etc.) and canned oil. Infection of dairy products can be associated with mastitis in cows or with purulent-inflammatory diseases of people related to the production of foods.

Thus, the abundance of various pathogenicity factors in staphylococci and their high allergic properties determine the pathogenesis of staphylococcal diseases, their nature, localization, severity of the course and clinical manifestations. Avitaminosis, diabetes, decreased immunity contribute to the development of staphylococcal diseases.

trusted-source[8], [9], [10], [11], [12], [13], [14], [15], [16]

Resistance of staphylococci

Among non-spore-forming bacteria, staphylococci, like mycobacteria, have the greatest resistance to external factors. They tolerate drying well and remain viable and virulent for weeks and months in the dryest minute dust, being a source of dust infection. Direct sunlight kills them only for many hours, and scattered acts very weakly. They are resistant to high temperatures: they heat up to 80 ° C for about 30 minutes, dry heat (110 ° C) kills them for 2 hours; low temperatures tolerate well. The sensitivity to chemical disinfectants varies greatly, for example, a 3% solution of phenol kills them for 15-30 minutes, and a 1% aqueous solution of chloramine in 2-5 minutes.

Epidemiology of staphylococcal infections

Since staphylococci are permanent inhabitants of the skin and mucous membranes, the diseases caused by them can have the character of either autoinfection (with various damages to the skin and mucous membranes, including microtraumas), or exogenous infection caused by contact-household, airborne, air-dust or alimentary (in food poisoning) ways of infection. Of particular importance is the carriage of pathogenic staphylococci, since carriers, especially in medical institutions (various surgical clinics, maternity hospitals, etc.) and in closed groups, can cause staphylococcal infections. Carrying of pathogenic staphylococci can have a temporary or intermittent nature, but a particular danger to others is represented by persons in whom it is permanent (resident carriers). In such people, staphylococci for a long time and in large numbers persist on the mucous membranes of the nose and throat. The reason for prolonged carriage is not entirely clear. It can be a consequence of the weakening of local immunity (a lack of secretory IgA), mucosal dysfunction, an increase in the adhesive properties of staphylococcus, or due to some other properties of it.

trusted-source[17], [18], [19], [20], [21], [22], [23], [24]

Symptoms of Staphylococcal Infections

Staphylococci easily penetrate the body through the smallest damage to the skin and mucous membranes and can cause a variety of diseases - from adolescent acne to severe peritonitis, endocarditis, sepsis, or septicopiaemia, in which lethality reaches 80%. Staphylococci cause furuncles, hydradenitis, abscesses, phlegmon, osteomyelitis; in wartime - frequent culprits purulent complications of wounds; Staphylococci play a leading role in purulent surgery. Possessing allergic properties, they can cause psoriasis, hemorrhagic vasculitis, erysipelas, nonspecific polyarthritis. Infection with staphylococcus food is a common cause of food poisoning. Staphylococci are the main culprits of sepsis, including those of newborns. In contrast to bacteremia (bacteria in the blood), which is a symptom of the disease and is observed in many bacterial infections, sepsis (septicemia - putrefaction) is an independent disease with a certain clinical picture, which is based on the damage to the organs of the reticuloendothelial system (mononuclear phagocyte system - CMF ). With sepsis, there is a purulent focus, from which the infectious agent periodically enters the blood, spreads through the body and affects the reticuloendothelial system (CMF), in the cells of which it multiplies, releasing toxins and allergens. In this case, the clinical picture of sepsis depends little on the type of pathogen, but is determined by the damage of certain organs.

Septicopyemia is a form of sepsis, in which the pathogen causes purulent foci in various organs and tissues, ie, sepsis complicated by purulent metastases.

Bacteremia in sepsis and septicopyemia can be short-lived and prolonged.

Postinfectious immunity exists, it is caused by both humoral and cellular factors. Antitoxins, antimicrobial antibodies, antibodies against enzymes, as well as T-lymphocytes and phagocytes play an important role in it. The intensity and duration of immunity against staphylococci have not been studied sufficiently, since their antigenic structure is too diverse, and there is no cross immunity.

Classification of staphylococci

The genus Staphylococcus includes more than 20 species, which are divided into two groups - coagulase-positive and coagulase-negative staphylococci. Various features are used to differentiate species.

Pathogenic to humans are mainly coagulase-positive staphylococci, but many coagulase negative substances can also cause diseases, especially in newborn babies (neonatal conjunctivitis, endocarditis, sepsis, urinary tract diseases, acute gastroenteritis, etc.). S. Aureus, depending on who is its main carrier, is divided into 10 ecowars (hominis, bovis, ovis, etc.).

Staphylococci have detected more than 50 types of antigens, antibodies are formed to each of them in the body, many of the antigens have allergenic properties. By specificity, antigens are divided into generic (common to all genus Staphylococcus); cross-reacting - antigens, common with iso-antigens of erythrocytes, skin and kidneys of the person (autoimmune diseases are associated with them); species and type-specific antigens. According to the type-specific antigens detected in the agglutination reaction, staphylococci are separated by more than 30 serovarants. However, the serological method of typing staphylococci has not yet been widely used. Species-specific include protein A, which forms S. Aureus. This protein is located superficially, it is covalently bound to peptidoglycan, its micrometer is about 42 kD. Protein A is especially synthesized in the logarithmic phase of growth at 41 ° C, thermolabile, not destroyed by trypsin; its unique property is the ability to bind to the Fc-fragment of IgG (IgGj, IgG2, IgG4) immunoglobulins, to a lesser extent with IgM and IgA. On the surface of protein A, several sites were identified capable of binding to a region of the immunoglobulin polypeptide chain located at the interface between the CH2 and CH3 domains. This property has found wide application in the coagglutination reaction: staphylococci, loaded with specific antibodies, in which active centers remain free, react with an antigen to give a rapid agglutination reaction.

The interaction of protein A with immunoglobulins leads to violations of the functions of complement and phagocyte systems in the patient's body. It has antigenic properties, is a strong allergen and induces the reproduction of T and B lymphocytes. Its role in the pathogenesis of staphylococcal diseases has not yet been fully clarified.

The strains of S. Aureus differ in sensitivity to staphylococcal phage. For the typing of S. Aureus, an international set of 23 moderate phages is used, which are divided into four groups:

  • 1 group - phages 29.52, 52A, 79, 80;
  • 2 group - phages 3a, 3C, 55, 71;
  • 3 group - phages 6, 42E, 47, 53, 54, 75, 77, 83A, 84, 85;
  • 4 group - phages 94, 95, 96;
  • outside groups - phage 81.

The ratio of staphylococci to phages is peculiar: one and the same strain can be lysed either by one phage or simultaneously by several. But since their sensitivity to phages is a sign of relatively stable, phagotyping of staphylococci has an important epidemiological significance. The disadvantage of this method is that no more than 65-70% of S. Aureus can be typed. In recent years, sets of specific phages have also been obtained for typing S. Epidermidis.

trusted-source[25], [26], [27]

Laboratory diagnostics of staphylococcal infections

The main method is bacteriological; Serologic reactions have been developed and introduced. If necessary (with intoxication) resort to a biological sample. Materials for bacteriological examination are blood, pus, mucus from the pharynx, nose, discharge of wounds, sputum (with staphylococcal pneumonia), feces (with staphylococcal colitis), in case of food intoxication - vomit, bowel movements, stomach washings, suspicious foods. The material is sown on blood agar (hemolysis), on milk-salt (milk-yolk-salt) agar (the growth of foreign bacteria is inhibited due to NaCl, pigment and lecithinase are better detected). The isolated culture is identified by species, it is determined by the presence of the main signs and pathogenicity factors (golden pigment, mannitol digestion, hemolysis, plasmacoagulase), necessarily check sensitivity to antibiotics, if necessary, perform phage typing. Among the serological reactions for the diagnosis of purulent-septic diseases are used RPGA and IFM, in particular for the detection of antibodies to teichoic acid or to species-specific antigens.

Three methods are used to determine the enterotoxigenicity of staphylococci:

  • serological - with the help of specific antitoxic sera in the precipitation reaction in the gel, an enterotoxin is detected and its type is established;
  • biological - intravenous infiltration of the filtrate of bovine staphylococcus culture to cats in a dose of 2-3 ml per 1 kg of weight. Toxins cause vomiting and diarrhea in cats;
  • an indirect bacteriological method is the isolation of a pure culture of staphylococcus from a suspected product and the determination of its pathogenicity factors (the formation of an enterotoxin correlates with the presence of other pathogenicity factors, in particular RNAase).

The most simple and sensitive is the serological method of detecting enterotoxin.

Treatment of staphylococcal infections

For the treatment of staphylococcal diseases, mainly beta-lactam antibiotics are used, to which sensitivity should first be determined. In severe and chronic staphylococcal infections, specific therapy - the use of autovaccine, anatoxin, anti-staphylococcal immunoglobulin (human), and antistaphylococcal plasma - has a positive effect.

Specific prophylaxis of staphylococcal infections

To create artificial immunity against staphylococcal infection staphylococcal anatoxin (liquid and tabletted) is used, but it creates antitoxic immunity only against staphylococci, mainly lysed by phages of Group I. The use of vaccines from killed staphylococci or their antigens, although leads to the emergence of antimicrobial antibodies, but only against those serovarcants from which the vaccine is made. The problem of finding a highly immunogenic vaccine, effective against many types of pathogenic staphylococci, is one of the most important problems of modern microbiology.

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