Also at risk are persons with immunodeficiency(HIV infection), drug addicts, people suffering from acute viral diseases(flu, hepatitis), diabetes mellitus, oncological diseases those with burns and injuries, undergoing treatment with corticosteroids and cytostatics, patients on hemodialysis.

How to get tested

For serological testing they take venous blood from the area of ​​the elbow, into a test tube with a gel containing a coagulation activator. Next, in the laboratory it is centrifuged to separate the serum, which is subsequently tested for the presence of antibodies. Donate blood only in the morning, on an empty stomach.

For polymerase chain reaction venous blood is taken into a test tube with an anticoagulant and examined by increasing the concentration nucleic acid repeated copying of a section of DNA.

For bacteriological analysis, a swab is usually taken from the throat and nose.

Other biological materials may also be used: sputum, breast milk, urine, feces, material from the wound surface, urogenital smear.

A swab from the throat and nose is taken in the morning, one sterile cotton swab is taken first from the nose, the other from the throat, then they are placed in test tubes containing a transport solution.

Main epidemic strains and clones MRSA

Staphylococci are well known as causative agents of purulent-septic infections in humans and animals. Along with family members Enterobacteriaceae they occupy a leading place in the etiology of purulent diseases. Genus Staphylococcus includes 35 various types. Depending on their ability to produce coagulase, the enzyme that causes coagulation of blood plasma, they are divided into two groups: coagulase-positive and coagulase-negative. The habitat of staphylococci is humans and warm-blooded animals, the external environment. Localization in humans - skin and mucous membranes, colon. Source staphylococcal infections is a sick person or a healthy carrier. Routes of transmission: airborne droplets, airborne dust, contact, food. Susceptibility to infection depends on general condition body and age. Children are most susceptible, especially newborns and infancy. Normally, the ability of staphylococcus to invade and the resistance of the host are well balanced, so the infection does not develop until a situation arises when a highly virulent microorganism or a macroorganism with reduced resistance is encountered.

Most well-known representative coagulase-positive staphylococci is S.aureus (Staphylococcus aureus). It occurs in the anterior nasal passages in 20–40% of healthy adults. In approximately 1/3 of the population, it is constantly discharged from the nose, 1/3 has a transient carriage, and 1/3 is free from carriage. S.aureus is most often isolated in purulent pathology and causes a number of diseases: folliculitis, boils and carbuncles, hydroadenitis, mastitis, wound infections, bacteremia and endocarditis, meningitis, pericarditis, pulmonary infections, osteomyelitis and arthritis, purulent myositis, food poisoning, syndrome toxic shock. The mentioned diseases are caused by pathogenicity factors: capsular polysaccharides, peptidoglycans and teichoic acids, protein A, enzymes, hemolysins, toxins (exfoliative, enterotoxins from A to E, H and I), superantigen, which belongs to the enterotoxin (TSST-1), causing toxic shock syndrome.

All other coagulase-positive staphylococci are isolated mainly from animals and rarely from humans, but in some cases they can cause purulent-inflammatory diseases in humans.

Among coagulase-negative staphylococci, they are the most significant in human pathology S. epidermidis And S. saprophyticus. They can cause urinary tract infections, osteomyelitis, bacteremia, infections in newborns in the wards intensive care, eye diseases, skin infections, affect heart valves, cause purulent inflammation during operations to replace heart valves with artificial ones, during organ bypass surgery, the use of intravenous catheters, catheters for hemodialysis, and also during angioplasty.

Currently, microorganisms of the genus Staphylococcus play a leading role among pathogens of nosocomial infections. Until a certain time, penicillin was the main drug of choice in the treatment of severe purulent infections called S. aureus. Then strains resistant to this antibiotic began to appear. It turned out that resistance to penicillin was due to the production of the enzyme lactamase, which destroys the β-lactam ring in the penicillin molecule. Currently, about 80% of isolated strains S. aureus synthesize β-lactamase. Instead of penicillin, in the case of isolation of penicillin-resistant strains, semi-synthetic penicillins resistant to β-lactamase are used. But since the 80s, strains begin to stand out S. aureus resistant to this group of antibiotics, in particular to oxacillin and methicillin. The resistance of such strains is associated with the production of penicillin binding protein (PBP 2a), the synthesis of which in turn is associated with the acquisition of the mecA chromosomal gene by staphylococci. Strains S. aureus Those possessing this gene exhibit resistance to all β-lactam antibiotics, including cephalosporins. S. aureus with the mentioned mechanism of resistance, the term methicillin-resistant strains is assigned. In some cases, resistance to semisynthetic penicillins may be due to overproduction of β-lactamases. In this case, resistance to semisynthetic penicillins when determined in laboratory conditions characterized as moderate. Methicillin-resistant strains S. aureus often show resistance to other antibiotics, particularly erythromycin and clindamycin. Due to their distribution in a number of foreign countries Vancomycin and teicoplanin are beginning to be used as antibiotics of choice. But already in 1996, the first reports of the isolation of strains appeared S. aureus with moderate resistance to vancomycin (MIC=8 μg/ml.), and since 2002, strains with high resistance (MIC>32 μg/ml.). Methicillin-resistant strains are also detected among S.epidermidis, and vancomycetes-resistant strains among S. haemolyticus.

For the treatment of purulent-septic infections caused by staphylococci, therapeutic bacteriophages are currently widely used, both monophages and combined ones, containing races of phages that lyse cells of several types of pathogens. Unlike antibiotics, they do not suppress the growth of normal human symbiotic microflora and do not lead to dysbiosis. However, it must be borne in mind that phages also cause the development of resistance in staphylococci, therefore, before their use, as well as before using antibiotics, it is necessary to check the sensitivity to them in isolated strains of staphylococci.

Indications for examination. Signs of purulent-septic infection, examination of medical personnel for carriage.

Material for research. Blood, CSF, pus, wound discharge, breast milk, nasal swabs; washouts from medical equipment and supplies.

Etiological laboratory diagnosis includes isolation of the pathogen on nutrient media, identification of its DNA.

Comparative characteristics of methods laboratory diagnostics, indications for the use of various laboratory tests. The technique for isolating the pathogen is now well established. Microorganisms are quite resistant to factors external environment, therefore, if the selected biological material cannot be immediately used for research, you can use special containers and transport media. More details about the technique of collecting and transporting biological material to the clinic. diagnostic laboratory is described in the section preanalytical stages of the study. As a rule, 3–4 days are enough to isolate the pathogen. An exception is the isolation of staphylococci from the blood. In this case, the success of the technique will largely depend on the right choice time for blood sampling and the presence of antibacterial drugs in the blood of patients.

Identification of a specific DNA fragment S. aureus, S. epidermidis, S. haemolyticus, S. saprophyticus The PCR method is used to study various biological materials. The results of DNA detection using the PCR method have a qualitative and quantitative format. It is possible to simultaneously detect and quantitation DNA methicillin-resistant S. aureus and methicillin-resistant coagulase-negative staphylococci. This study is simple and reproducible, which allows optimizing epidemiological surveillance of the spread of methicillin-resistant strains, significantly reducing the time and labor intensity of the study. However, identifying a specific DNA fragment S. aureus, S. epidermidis, S. haemolyticus, S. saprophyticus The PCR method does not allow identifying viable microorganisms or determining their sensitivity to antibiotics.

Features of interpretation of laboratory research results. When examining sterile biological material (blood, CSF) clinical significance has detection S. aureus in any concentration. In non-sterile biological material, only high concentrations S. aureus, meaning its leading role in the inflammatory process.

Methicillin-resistant Staphylococcus aureus - pathogens of nosocomial infections: identification and genotyping

DEVELOPED: Federal Service for Supervision of Consumer Rights Protection and Human Welfare (G.F. Lazikova, A.A. Melnikova, N.V. Frolova); State institution "Research Institute of Microbiology and Epidemiology named after N.F. Gamaleya RAMS" Moscow (O.A. Dmitrenko, V.Ya. Prokhorov., Academician of the Russian Academy of Medical Sciences A.L. Ginzburg).


I APPROVED

Deputy Head of the Federal Service for Supervision of Consumer Rights Protection and Human Welfare L.P. Gulchenko July 23, 2006

1 area of ​​use

1 area of ​​use

1.1. These guidelines provide information on the role of methicillin-resistant strains Staphylococcus aureus in the occurrence of nosocomial infections, their microbiological and epidemiological features, traditional and molecular genetic methods of identification and typing are outlined.

1.2. Methodological recommendations have been developed to assist specialists of bodies and institutions carrying out state sanitary and epidemiological supervision, and medical institutions organizing and carrying out preventive and anti-epidemic measures to combat nosocomial infections.

2. Normative references

2.1. Federal Law "On the Sanitary and Epidemiological Welfare of the Population" N 52-FZ of March 30, 1999 (as amended December 30, 2001, January 10, June 30, 2003, August 22, 2004)

2.2. Regulations on the State Sanitary and Epidemiological Service of the Russian Federation, approved by Decree of the Government of the Russian Federation No. 554 of July 24, 2000.

2.3. Resolution No. 3 of October 5, 2004 “On the state of incidence of nosocomial infectious diseases and measures to reduce them.”

2.4. Guidelines MU 3.5.5.1034-01 * “Disinfection of test material infected with bacteria of I-IV pathogenicity groups when working using the PCR method.”
________________
* In the territory Russian Federation the document is not valid. MU 1.3.2569-09 is in effect. - Database manufacturer's note.

2.5. Guidelines MUK 4.2.1890-04 "Determination of the sensitivity of microorganisms to antibacterial drugs."

2.6. Guidelines for epidemiological surveillance of nosocomial infections dated 09/02/87. N 28-6/34.

3. General information

In the last decade, the problem of nosocomial infections (HAIs) has become exclusively great importance for all countries of the world. This is due, first of all, to a significant increase in the number of hospital strains of microorganisms that are resistant to a wide range of antimicrobials. Despite significant underreporting, about 30 thousand cases of nosocomial infections are registered annually in the Russian Federation, with minimal economic damage amounting to more than 5 billion rubles annually. Among the causative agents of nosocomial infections, one of the first places still belongs to microorganisms of the genus Staphylococcus, the most pathogenic representative of which is S. aureus. The epidemiological situation is complicated due to the widespread spread in hospitals, as well as the appearance in the community environment of clinical isolates S. aureus oxacillin-resistant (ORSA or MRSA). MRSA can cause a variety of clinical forms nosocomial infections, including the most severe, such as bacteremia, pneumonia, septic shock syndrome, septic arthritis, osteomyelitis and others, which require long-term and expensive treatment. The emergence of complications caused by MRSA leads to an increase in hospitalization time, mortality rates, and significant economic losses. It has been shown that the increase in the frequency of nosocomial infections observed in hospitals around the world is due to the spread of epidemic strains of MRSA, many of which are capable of producing pyrogenic toxins - superantigens that suppress the immune response to S. aureus.

Since the late 90s of the last century, in Russian hospitals there has been an increase in the frequency of MRSA isolation, which in a number of hospitals has reached 30-70%. This makes the use of many antimicrobial drugs ineffective and significantly worsens the quality of medical care to the population. In these conditions, improving methods of epidemiological and microbiological monitoring aimed at identifying epidemically significant strains is becoming increasingly important.

4. Characteristics of MRSA as pathogens of nosocomial infections

4.1. Taxonomy and biological features

In recent years, there has been a clear trend of growth in nosocomial infections caused by opportunistic gram-positive microorganisms and, in particular, representatives of the genus Staphylococcus. According to the 9th edition of Bergey's Guide to Bacteria (1997), staphylococci are classified as gram-positive facultative anaerobic cocci along with the genera Aerococcus, Enterococcus, Gemella, Lactococcus, Leuconostoc, Melissococcus, Pediococcus, Saccharococcus, Stomatococcus, Streptococcus, Trichococcus And Vagococcus. Staphylococci are distinguished from other representatives of this group by a set of properties, including the characteristic grape-shaped interposition of microbial cells in culture, the ability to grow in the temperature range from 6.5 to 45 ° C, with a pH in the range of 4.2-9, 3, in the presence increased concentrations NaCl (up to 15%) and 40% bile. Staphylococci have pronounced biochemical activity. They are catalase-positive, reduce nitrate to nitrite or nitrogen gas, hydrolyze proteins, hippurate, fats, tween, break down big number carbohydrates under aerobic conditions with the formation acetic acid and small amounts of CO, however, esculin and starch, as a rule, are not hydrolyzed and do not form indole. When cultivated under aerobic conditions, they require amino acids and vitamins; when cultivated under anaerobic conditions, they require additional uracil and fermentable carbon sources. The cell wall contains two main components - peptidoglycan and associated teichoic acids. The composition of peptidoglycan includes a glycan built from repeating units: N-acetylglucosamine and N-acetylmuramic acid residues, to the latter in turn are attached peptide subunits consisting of N (L-alanine-D-isoglutamyl)-L-lysyl-D- residues. alanine The peptide subunits are cross-linked by pentapeptide bridges consisting exclusively or mainly of glycine. Unlike other gram-positive facultative anaerobic cocci, staphylococci are sensitive to the action of lysostaphin, an endopeptidase that hydrolyzes glycyl-glycine bonds in the interpeptide bridges of peptidoglycan, but are resistant to the action of lysozyme. Content of guanidine+cytosine in the DNA structure Staphylococcus at the level of 30-39% indicates phylogenetic proximity to genera Enterococcus, Bacillus, Listeria And Planococcus. Genus Staphylococcus has 29 species, the most pathogenic among them both for humans and for many mammals is the species Staphylococcus aureus. This is explained by the ability of representatives of this species to produce a large number of extracellular products, which include numerous toxins and enzymes involved in colonization and development infectious process. Almost all strains secrete a group of exoproteins and cytotoxins, which includes 4 hemolysins (alpha, beta, gamma and delta), nucleases, proteases, lipases, hyaluronidases and collagenases. The main function of these enzymes is to convert host tissues into a nutrient substrate necessary for the proliferation of the microbe. Some strains produce one or more additional exoproteins, these include toxic shock syndrome toxin, staphylococcal enterotoxins (A, B, Cn, D, E, G, H, I), exfoliative toxins (ETA and ETB), and leukocidin. The most famous taxonomically significant characteristic S. aureus is the ability to coagulate blood plasma, which is due to the production of an extracellular secreted protein with a molecular weight of about 44 kDa. By interacting with prothrombin, plasmacoagulase activates the process of converting fibrinogen into fibrin. The resulting clot protects microbial cells from the action of bactericidal factors of the macroorganism and provides a favorable environment for their reproduction. Subsequently, as a result of the dissolution of the fibrin clot, multiplied microorganisms enter the bloodstream, which can lead to the development of generalized forms of infection. In the 8th edition of Bergey's Guide to the Identification of Bacteria (1974), staphylococci were characterized as microorganisms usually sensitive to antibiotics such as β-lactams, macrolides, tetracyclines, novobiocin and chloramphenicol, and resistant to polymyxin and polyenes. This position was refuted by the widespread spread of first penicillin-resistant and subsequently methicillin-resistant strains. The first semi-synthetic penicillin, methicillin, resistant to the action of staphylococcal β-lactamase, was intended for the treatment of infections caused by penicillin-resistant strains. However, less than two years after its introduction into medical practice in 1961, the first reports of the isolation of methicillin-resistant strains of Staphylococcus aureus (MRSA) appeared. They became a problem for specialists only in the mid-70s - early 80s of the last century, when it became obvious that, having all the characteristic morphological, cultural, physiological and biochemical properties characteristic of Staphylococcus aureus, MRSA have their own biological features. First, the unique biochemical mechanism of resistance to methicillin provides them with resistance to all semisynthetic penicillins and cephalosporins. Secondly, such strains are capable of “accumulating” antibiotic resistance genes and therefore are often resistant to several classes of antimicrobial drugs at the same time, thereby significantly complicating the treatment of patients. And finally, thirdly, such strains are capable of epidemic spread and cause severe forms nosocomial infections. Although methicillin was replaced by oxacillin or dicloxacillin in subsequent years, the term MRSA has become firmly established in the scientific literature.

4.2. Clinical significance

Currently, MRSA are the leading causative agents of nosocomial infections in hospitals in many countries around the world. The frequency of their isolation in hospitals in the USA, Japan, and many Western European countries reaches 40-70%. The only exceptions seem to be a number of Scandinavian countries, where strict anti-epidemic measures have historically been taken to control the spread of such strains. In hospitals of the Russian Federation, the frequency of MRSA isolation ranges from 0 to 89%. The highest frequency of release is observed in intensive care, burn, trauma and surgical departments hospitals located in large cities. One of the main reasons for this pattern is the concentration of patients with integrity disorders in such hospitals. skin and damaged immunological barriers. The most common site of infection is postoperative and burn wounds and Airways. Primary and secondary bacteremia are observed in approximately 20% of infected patients. In the case of infection in burn patients, the frequency of bacteremia often increases to 50%. Factors contributing to the development of bacteremia include the presence of a central venous catheter, anemia, hypothermia and nasal carriage. The development of bacteremia significantly increases the likelihood of death. Mortality due to bacteremia is particularly high among patients in burn units and intensive care units, where it can reach 50% compared with 15% in the control group. The risk of death is almost threefold higher among patients with MRSA bacteremia compared with patients infected with methicillin-susceptible strains. S. aureus. The development of hospital-acquired bacteremia leads to a significant increase in the cost of hospitalization. IN modern conditions Treatment of such patients usually requires intravenous administration vancomycin, teicoplanin or linezolid, however clinical effectiveness these drugs are often significantly lower than those of antibiotics used to treat patients with complications caused by methicillin-sensitive S. aureus. According to the US Centers for Disease Control, the average length of stay for a patient with surgery is 6.1 days, while for complications caused by MRSA it increases to 29.1 days, with average costs increasing with $29,455 to $92,363 per case.

Diseases caused by MRSA can begin during treatment with antibiotics, including aminoglycosides and cephalosporins. In this regard, it should be noted that inadequate prescription of antibiotics in cases of severe nosocomial infections dramatically worsens the prognosis of the disease. Mortality from complications caused by MRSA varies significantly and depends on both the age of the patient and concomitant disease(arterial hypertension, diabetes, etc.), and from the addition of additional microflora. The most common secondary manifestations of MRSA infection are endocarditis, hematogenous osteomyelitis, and septic arthritis. One of the most serious complications caused by MRSA is toxic shock syndrome (TSS). Clinical manifestations TSS include the following symptom complex: hyperthermia, rash, vomiting, diarrhea, hypotension, generalized edema, acute respiratory distress syndrome, multiple organ failure, disseminated intravascular coagulation. TSS can develop as a complication after childbirth, surgery, or superinfection S. aureus tracheal damage caused by influenza virus. The recently described staphylococcal scarlet fever and persistent epithelial desquamation syndrome are considered variants of TSS.

4.3. Pathogenicity factors and virulence

Many epidemic MRSA strains produce pyrogenic toxins with superantigen activity (PTSAgs), which include enterotoxins A, B, C and toxic shock syndrome toxin (TSST-1). By interacting with the variable region -chain of T-cell receptors, PTSAgs activate a significant population (10-50%) of T-lymphocytes, which leads to the release large quantity cytokines. Superantigens are capable of destroying endothelial cells and can eliminate neutrophils from areas of inflammation. They cause or complicate the pathogenesis of acute and chronic diseases humans, such as septic shock, sepsis, septic arthritis, glomerulonephritis and some others. Non-menstrual toxic shock syndrome can be associated not only with strains producing TSST-1, but also with strains producing enterotoxins A, B and C. It should be borne in mind that recognition of post-surgical toxic shock is often difficult due to the absence of signs characteristic of Staphylococcus aureus suppuration in the area of ​​the surgical wound. There has been a correlation between sensitization by staphylococcal enterotoxins A and B and the severity of diseases such as allergic rhinitis, atopic dermatitis, bronchial asthma, reactive arthritis. The genes that determine the synthesis of PTSAgs may be located on mobile genetic elements (bacteriophage “pathogenicity islands”) within the MRSA chromosome.

The virulence of MRSA remains controversial. They practically do not cause disease in healthy medical personnel. However, numerous studies have shown that the prognosis for severe forms of nosocomial infections, such as pneumonia and bacteremia, is significantly worse among patients infected with MRSA compared with patients infected with methicillin-sensitive S. aureus.

4.4. Genetic control of methicillin resistance and phenotypic expression features

The targets of β-lactam antibiotics (both penicillins and cephalosporins) are trans- and carboxypeptidases - enzymes involved in the biosynthesis of the main component of the cell wall of microorganisms - peptidoglycan. Due to their ability to bind to penicillin and other β-lactams, these enzymes are called penicillin-binding proteins (PBPs). U Staphylococcus aureus there are 4 PSBs, differing in both molecular weight, and by functional activity. The resistance of methicillin-resistant strains of Staphylococcus aureus (MRSA) to β-lactam antibiotics is due to the production of an additional penicillin-binding protein, PSB-2, which is absent in sensitive microorganisms. When the β-lactam antibiotic suppresses the activity of the main penicillin-binding proteins, PSB-2, due to its lower affinity for drugs of this group continues to function and maintains the viability of the microbial cell. The synthesis of PSB-2" is encoded by the gene mec A, located on the chromosome S. aureus, in a specific region found only in methicillin-resistant strains of staphylococcus - mec DNA. Months DNA represents a new class of mobile genetic elements called the staphylococcal chromosome cassette mec(Staphylococcal chromosomal cassette mec=SCC mec). The existence of 4 types of SCC has been revealed mec, differing both in size (from 21 to 66 kb) and in the set of genes that make up these cassettes. The division into types is based on differences in the genes that form the complex itself mec, and in a set of genes encoding recombinases ccrА And ccrВ included in various combinations into the staphylococcal chromosome cassette (Fig. 1). Complex mec may include: mecА- structural gene that determines the synthesis of PSB-2"; memecА; mecR1- a gene that transmits a signal into the cell about the presence of a -lactam antibiotic in the environment; as well as insertion sequences IS 43 1 and IS 1272 . There are currently 4 known variants of the complex mec(Fig. 2).

Fig.1. SCCmec types

Characteristics of SCC types mec

Fig.1. SCC types mec

Fig.2. Genetic structure of mec complexes of different classes

Genetic structure of complexes mec various classes

Class A, IS431 - mec A- mec R1- mec 1

- Class B, IS431 - mec A- mec R1-IS1272

- Class C, IS431 - mec A- mec R1-IS431

- Class D, IS431 - mec A- mec R1

Fig.2. mecА- structural gene that determines the synthesis of PSB-2"; me cI - regulatory gene influencing transcription mecА;
mecR1 - a gene that transmits a signal into the cell about the presence in the environment -lactam antibiotic; IS431 and IS1272 - insertion sequences

Additionally, differences between cassette types mec are caused by the presence of a number of additional genes located in the genetic regions J1a, J1b.

The uniqueness of methicillin resistance also lies in the existence of the phenomenon of heteroresistance, the essence of which is that under incubation conditions at 37 °C, not all cells of the population exhibit resistance to oxacillin. The genetic control of the heteroresistance phenomenon has not yet been fully elucidated. It is only known that the expression of resistance can be influenced by regulatory genes - lactamase, as well as a number of additional genes, the so-called fem (factors essential for methicillin resistance) or aux, localized in various parts chromosomes S. aureus, outside SCC mec. The complexity of regulation is manifested in phenotypic differences. There are 4 stable phenotypes (classes) of resistance. The first three classes are heterogeneous. This means that in the populations of staphylococci belonging to these classes, there are subpopulations of microbial cells with different levels of resistance. In this case, staphylococcal clones obtained from isolated colonies (formed during sieving of the primary culture) completely coincide in population composition with the original culture.

Class 1. The growth of 99.99% of cells is suppressed by oxacillin at a concentration of 1.5-2 μg/ml, the growth of 0.01% of microbes is suppressed only at 25.0 μg/ml.

Class 2: 99.9% of cells are inhibited at oxacillin concentrations of 6.0-12.0 µg/mL, while 0.1% of microbes are inhibited at concentrations >25.0 µg/mL.

Class 3. The growth of 99.0-99.9% of cells is inhibited at a concentration of 50.0-200.0 μg/ml and only the growth of 0.1-1% of the microbial population is suppressed at an oxacillin concentration of 400.0 μg/ml.

Class 4. Representatives of this class are characterized by a homogeneous level of resistance that exceeds 400.0 μg/ml for the entire population.

Due to the presence of heterogeneity in oxacillin resistance, it may be difficult to identify MRSA using traditional microbiological methods.

4.5. Features of the epidemiology of MRSA

Using various molecular genetic typing methods, it has been established that the global spread of MRSA is epidemic. Unlike methicillin-sensitive S. aureus, the vast majority of clinical MRSA isolates belong to a limited number of genetic lineages or clones. Identified in different hospitals various groups researchers they initially received and different names(Table 1). Thus, epidemic strains EMRSA1-EMRSA-16 were first identified by English researchers, and epidemic clones: Iberian, Brazilian, Japanese-American, pediatric - by a group of American researchers led by G. de Lencastre. It should be borne in mind that there is no clear gradation between the concepts of epidemic strain and epidemic clone. According to commonly used terminology, a strain that has caused three or more cases of illness among patients in several hospitals is considered epidemic. An epidemic clone is an epidemic strain that has spread to hospitals in countries on different continents. However, many of the epidemic strains initially identified in the UK have become de facto epidemic clones due to their wide geographical distribution. Using the method of sequencing internal fragments of 7 “housekeeping” genes for typing, i.e. genes responsible for maintaining the life of a microbial cell (multilocus sequencing method) made it possible to establish that these numerous clones belong to only 5 phylogenetic lines or clonal complexes: CC5, CC8, CC22, CC30, CC45. Within clonal complexes, division into groups or sequence types is possible, which differ by 1-3 mutations or recombinations in the structure of sequenced genes. A fairly strict relationship has been established between MRSA belonging to a certain genetic “background” and the content of a certain type mec DNA. The most diversified and numerous are the clonal complexes CC5 and CC8, which contain epidemic clones with various types SCC mec. At the same time S.C.C. mec Type IV may be present in a variety of backgrounds. Particularly abundant is the St239 group, which represents a separate branch within the CC8 clonal complex. This group includes various epidemic strains and clones: EMRSA-1, -4, -7, -9, -11, Brazilian, Portuguese (Table 1). Currently, an epidemic spread of MRSA strains genetically related to EMRSA-1 (Brazilian clone) and Iberian clone has been identified in Russian hospitals.

Table 1

Major epidemic strains and clones of MRSA

Once introduced into a hospital setting, MRSA can survive there for a long time. This determines the strategy of anti-epidemic measures: it is very important to prevent the introduction and spread of epidemic strains in the hospital.

It should be noted that the epidemic strain that dominates in certain areas periodically changes. Thus, according to the staphylococcal reference laboratory in Colindale (London), in 1996, strains EMRSA-15 and EMRSA-16 were responsible for more than 1,500 incidents involving three or more patients in 309 hospitals in England, while the remaining epidemic strains were responsible for only 361 incidents in 93 hospitals. The spread of these epidemic strains led to a 15-fold increase in MRSA mortality and a 24-fold increase in bacteremia rates between 1993 and 2002. according to data from the UK Department of National Statistics.

The spectrum of antibiotic resistance of epidemic MRSA strains continues to increase. They acquire resistance to drugs from the fluoroquinolone group much faster than methicillin-sensitive ones. A characteristic feature of many epidemic MRSA strains is resistance to almost all known classes of antimicrobial drugs, with the exception of glycopeptides and oxazolidinones. In recent years, cases of isolation of MRSA isolates that are moderately sensitive to vancomycin and even vancomycin-resistant have become more frequent. The spread of such strains in Russian hospitals could have dramatic consequences.

Closely intertwined with the problem of hospital-acquired MRSA strains is the problem of non-hospital-acquired MRSA. These strains do not yet have multiple resistance to antibiotics, are genetically different from hospital strains, and their origin remains unknown. It is assumed that they were formed from sporadic hospital strains. Community-acquired strains of MRSA are capable of causing a necrotizing form of pneumonia characterized by extreme severe course and requiring hospitalization of the patient, which creates a threat of the introduction and spread of such strains in hospitals.

Reservoirs and sources of infection

The main reservoir and source of infection in the hospital environment are both infected and colonized patients. Factors contributing to MRSA infection in patients are: prolonged hospital stay, inappropriate antibiotic prescription, taking more than one antibiotic, and duration of antibiotic therapy for more than 20 days. If infection is suspected, a microbiological examination of the wound discharge is necessary. skin lesions, manipulation sites, intravenous catheter, tracheostomy and other types of stomas, blood, sputum, and urine in catheterized patients. In case of colitis or enterocolitis associated with taking antibiotics, it is necessary to conduct a stool examination.

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They belong to the Micrococcoceae family. The genus Staphylococcus includes 19 species, of which only a few are pathogenic for humans: S.aureus, S.epidermidis and S.saprophyticus. Diseases are caused by aureus, less often by epidermal and even less often by saprophytic staphylococci.

Morphology, physiology. Individual cells have the shape of a regular ball; when they multiply, they form clusters in the form of bunches of grapes (slaphyle - bunch of grapes). Size from 0.5 to 1.5 microns. In preparations from pathological material (from pus) they are located singly, in pairs or in small clusters. Staphylococcus aureus has the ability to form a delicate capsule.

Staphylococci are facultative anaerobes, but develop better under aerobic conditions, Gr+. On the surface of dense nutrient media they form round, convex, pigmented (golden, fawn, lemon yellow, white) colonies with smooth edges; in liquids - uniform turbidity. In laboratories, they use the ability of staphylococci to multiply in environments with large amounts (6-10%) of NaCl ( JSA). Other bacteria cannot tolerate such a concentration of salt; salt environments are selective for staphylococci. Strains of Staphylococcus aureus that produce hemolysins give colonies on blood agar, surrounded by a zone of hemolysis.

Staphylococci have a number of enzymes that break down many carbohydrates and proteins. The test for glucose fermentation under anaerobic conditions has differential diagnostic significance. Of the enzymes involved in the pathogenesis of staphylococcal infections, only plasmacoagulase and partially DNase are characteristic of S. aureus. Other enzymes (hyaluronidase, proteinase, phosphatase, muromidase) are variable (but are more often produced by S.aureus). Staphylococci synthesize bacteriocins. Resistant to penicillin (penicillinase).

Antigens. Cell wall substances: peptidoglycan, teichoic acids, protein A, type-specific agglutinogens, as well as a capsule of polysaccharide nature. Peptidoglycan shares common antigens with peptidoglycans from micrococci and streptococci. The antigenicity of teichoic acids is associated with amino sugars. Protein A of Staphylococcus aureus is capable of nonspecific binding to the Fc fragment of IgG, and therefore it is agglutinated by normal human serum. Staphylococci have 30 protein type-specific antigens. But intraspecific differentiation by Ar structure is not used in practice.

Pathogenicity. Toxins and enzymes have a damaging effect on the cells and tissues of the human body. Pathogenicity factors also include the capsule, which prevents phagocytosis and fixes complement, as well as protein A, which inactivates complement and inhibits opsonization when interacting with the Fc fragment of IgG.

S.aureus is capable of secreting a number of toxins, in particular leukocidin, which has a detrimental effect on phagocytic cells, mainly macrophages. Hemolysins (α, β, delta, γ) have a lysing effect on human and animal erythrocytes (rabbit, horse, sheep). The main one is α-toxin produced by S. aureus. In addition to hemolytic, this poison has a cardiotoxic effect and causes spasms coronary vessels and cardiac arrest in systole, it affects nerve cells and neurons, lyses cell membranes and lysosomes, which leads to the release of lysosomal enzymes.

The occurrence of staphylococcal food poisoning is associated with the action of enterotoxins produced by Staphylococcus aureus. There are 6 known antigens of various enterotoxins (ABCDEF).

Exfoliative toxins cause pemphigus, local bullous impetigo, and a generalized scarlet-like rash in newborns. The diseases are accompanied by intraepidermal detachment of the skin epithelium, the formation of merging blisters, the fluid in which is sterile. The focus of staphylococcal infection is most often in the umbilical wound.

Exoverments: plasmacoagulase carries out plasma coagulation (proteins seem to be dressed in a fibrous cover that protects them from phagocytosis). Large concentrations of coagulase in the patient’s body lead to a decrease in peripheral blood clotting, hemodynamic disturbances, and progressive oxygen starvation of tissues.

Hyaluronidase promotes the spread of staphylococci in tissues. Lecithinase destroys lecithin, which is part of cell membranes, causing leukopenia. Fibrinolysin dissolves fibrin, delimiting the local inflammatory focus, which contributes to the generalization of the pathological process. The pathogenetic properties of other staphylococcal exoenzymes (DNase, muramidase, proteinase, phosphatase), which often accompany coagulase activity, have not yet been determined.

Ecology and distribution. In the first days of a person’s life, staphylococci settle on the mucous membranes of the mouth, nose, intestines, as well as on the skin, and are part of the emerging normal microflora of the human body.

Staphylococci constantly enter the environment from a person. They are present on household items, in the air, in water, in soil, and on plants. But their pathogenic activity is different, Special attention is given to Staphylococcus aureus as potentially pathogenic for humans. Upon contact with a source of infection, not all people become carriers of S. aureus. The formation of bacterial carriage is facilitated by the low content of SIgA in nasal secretions and other manifestations of functional failure immune system. In such persons, resident carriage is formed, i.e. The nasal mucosa becomes the permanent habitat of staphylococci, on which microorganisms multiply intensively and are released into the environment in massive doses. IN medical institutions their source is patients with open purulent-inflammatory processes (the infection is transmitted by contact). This is facilitated by the long survival of staphylococci on surrounding objects.

They tolerate drying well, the pigment protects them from the harmful effects of sunlight (direct sunlight kills them only after a few hours). At room temperature, they remain viable on patient care items for 35–50 days, and on hard equipment for tens of days. When boiled, they die instantly, are sensitive to disinfectants, to brilliant green, which allows it to be widely used for the treatment of superficial inflammatory skin diseases.

Pathogenesis of human diseases. Capable of infecting any tissue of the human body. These are local purulent-inflammatory processes (furuncles, carbuncles, wound suppuration, bronchitis, pneumonia, otitis media, sore throat, conjunctivitis, meningitis, endocarditis, enterocolitis, food poisoning, osteomyelitis). The generation of any form of local process ends with sepsis or septicopyemia. People with immunodeficiency conditions develop staphylococcal infections more often.

Immunity. Adults are resilient because... have natural protective mechanisms and specific antibodies that are acquired throughout life through contact with patients and carriers. In the process of staphylococcal infection, sensitization of the body occurs.

Both antimicrobial, antitoxic and antienzyme antibodies are important in the formation of immunity. The degree of protection is determined by their titer and site of action. Secretory IgA plays an important role, providing local immunity of the mucous membranes. Antibodies to teichoic acids are detected in the blood serum of adults and children with severe staphylococcal infections: endocarditis, osteomyelitis, sepsis.

Laboratory diagnostics. The material (pus) is subjected to bacterioscopy and sown on nutrient media. Blood, sputum, and feces are examined using the bacteriological method. After isolating a pure culture, the species is determined based on a number of characteristics. In the case of S.aureus isolation, plasmacoagulase, hemolysin, and A-protein are determined.

Serodiagnosis: RP (alpha toxin), RNGA, ELISA.

To establish the source and routes of spread of infection, isolated cultures are phagotyped. Laboratory analysis certainly includes determining the sensitivity of the isolated culture or cultures to antibiotics.

Prevention and treatment. Prevention is aimed at identifying S.aureus carriers, mainly among personnel medical institutions, for the purpose of their rehabilitation. Particular attention is paid to the prevention of staphylococcal infections in newborns.

For the treatment of acute staphylococcal diseases, antibiotics are prescribed, the choice of which is determined by the sensitivity of the isolated culture to a set of drugs. For septic processes, anti-staphylococcal immunoglobulin or anti-staphylococcal plasma is administered. For the treatment of chronic staphylococcal infections (chroniosepsis, furunculosis, etc.), staphylococcal toxoid and autovaccine are used, which stimulate the synthesis of antitoxic and antimicrobial antibodies.