HISTORY:
In 1874, the Viennese surgeon Christian Billroth observed in lesions of erysipelas a microorganism shaped chains.
In 1875, Louis Pasteur observed this organism in vaginal secretions and blood of patients suffering from puerperal fever, but in 1869 in Strasbourg Coze and Feitz had observed during an epidemic of puerperal fever, many “points” in chains in the blood of a dead woman.
In 1884, Rosenbach accurately describes Streptococcus pyogenes.
At the beginning of this century, Schottmuller is a relationship between the nature of hemolytic strains and pathogenicity; Brown then used hemolysis as a classification criterion.
In 1933, Rebecca Lancefield establishes the modern classification of streptococci based andgéniques properties of carbohydrates.
1 – GENERAL CHARACTERISTICS STREPTOCOCCI:
The genus Streptococcus gathers bacterial species that share a certain number of characters.
They are Gram-positive cocci, spherical or ovoid, pair arranged to form diplococci and may be in the form of long chains sometimes they do not sporulate.
2. Their metabolic properties:
– They have no catalase (unlike staphylococci), or oxidase (unlike Neisseria).
– They can grow aerobically, have a fermentative metabolism and are considered tolerant anaerobic oxygen.
Strict anaerobic bacteria have the same morphology and belong to the genusPeptostreptococcus.
The Streptococcus genus includes many species. One of them Streptococcus pneumoniae, because of its clinical importance and its special features will be considered separately.
Among others, it is individuals who share common points that earned them to be brought together in a new genusEnterococcus.
Finally, it has recently been proposed to group the lactic streptococci in the genus Lactococcus.
The table below shows the bacteriological features that distinguish Streptococcus pneumoniae other streptococci.
II – CLASSIFICATION:
II is no single criterion by which to classify the different species of the genus Streptococcus.
The classification involves the study of three types of bacteriological characters.
1. Hemolysis:
It allows to distinguish strains, p or non-haemolytic (y). This old test today has a value orientation.
2. Lancefield classification (1933):
It is based on immunological criteria to detect specific group antigens.
Most streptococcal species, including beta-hemolytic, have in their wall polysaccharide C, the composition and the antigenic properties used to define serogroups.
Lancefield classification distinguishes 20 serogroups (designated by letters A to H and K W).
Some species are devoid of this polysaccharide antigen; these are often non-haemolytic or giving a so-called hemolysis viridans strains.
They therefore can not be classified by the method of Lancefield.
These nongroupables streptococci are classified in cash through the study of their cropping and metabolic characters.
3. Metabolic cropping and metabolic characteristics:
They allow you to categorize nongroupables species by the method of Lancefield but also within some Lancefield groups to recognize different species: it is the case for example of group C which consists of four species: S. equi, S. equisimilis, S. dysgalactiae and S. zooepidemicus.
4. Recently it emerged that classifications should consider other criteria such as GC%:
comparison of 16S ribosomal RNA, DNA-DNA hybridization, the composition of the wall (murein type) and type of menaquinone (Schleifer and Klipper-Balz).
D resulted from these elements combined with the above criteria as Streptococcus had burst into three genera. Strict sense Streptococcus, Enterococcus, Lactococcus and Streptococcus Within there are Streptococcus pyogenes, oral flora and other streptococci (Table II) .
III – HABITAT:
Streptococci are ubiquitous.
Some of them are found in the external environment. They can survive in it; and the discovery of enterococci in water or food sign fecal contamination from human or animal origin.
Others are more fragile and live in the commensal state at the integuments or mucous membranes of humans or animals. Enterococci and more resistant viridans streptococci are constant commensal of the digestive tract and oral flora.
The normal presence of streptococci in mucocutaneous level says they can frequently contaminate samples and build dirt.
Recently an outbreak of infections with S. pyogenes foodborne has been described.
IV – PATHOPHYSIOLOGY:
A – The role of adhesion:
The development of a streptococcal infection depends adhesion capacity of the bacteria to the surface of cells in the body. Bacteria bind to cell surfaces through fimbriae, surface proteins, lipoteichoic acids, perhaps protein M. These structures play an important role in adherence of streptococci. So for streptococci, antibodies against group antigens, type or teichoic acids reduce adhesion.
For the oral streptococci, high molecular weight polymers, such as dextrans and levans (MW> 200 000), play an important role in the attachment of these streptococci (S. sanguis …) after bacteremia in cardiac tissue or onsite at the plaque (5. mutans …). In the latter case, the synthesis of dextran is from glucose or sucrose under the influence of glucosyl transferase or fructosyl transferase.
It has been shown by experimental endocarditis is a relationship between the ability to produce dextran and the ability to cause endocarditis. Membership in the cardiac tissue requires a minimum number of bacteria. This binding is rapid and bacteria within 24 hours covered with fibrin, which protects the phagocytosis. Only surface bacteria are metabolically active. Those that are embedded in fibrin vegetations or have decreased activity, they are more difficult to destroy by antibiotics.
The production of dextran by oral streptococci (S. mutans and S. sanguis) allows these species to adhere to tooth enamel and promotes the adherence of other bacterial species through the surface polysaccharide fibers that are ” glycocalyx. “ This explains that if S. sanguis and S. mutans represent 90% of the flora of the plate, including other anaerobic species are present. Dextrans and levans present are degraded by bacteria in plaque. They are metabolized by entering the cycle of fermentation with production of pyruvic acid, lactic acid, propionic, butyric … which result in the destruction of apatite crystals of enamel, which will be followed by an organic disorganization of enamel so caries.
B – Rheumatic fever:
To explain rheumatic fever due to group A streptococci (S. pyogenes) two theories exist:
1. The first autoimmune theory is substantiated by:
– The existence of a latency period between streptococcal infection and the development of arthritis.
The exaggeration of the antibody response in patients with rheumatic fever compared to others.
The reaction of A streptococcal antibodies vis-à-vis the myofibrils and heart valves with deposition of immune complexes and complement in these structures, and subthalamic neurons and caudate nuclei of the central nervous system. Likewise we find an increase in immunoglobulin levels and a decrease rate of Cl, C3 and C4 in the synovial fluid of subjects with rheumatoid arthritis.
2. The second hypersensitivity theory:
The sensitized T cells could react with streptococcal antigens and release lymphokines exaggerated amount. Argue in favor of this hypothesis, increased lymphocyte proliferative response during outbreaks of rheumatic fever but an association of this response with a genetic predisposition to certain individuals related to tissue groups (HLA-A 35).
However it is the theory of an autoimmune disease that is often advanced.
C – Post-streptococcal glomerulonephritis:
The pathophysiology of acute post-streptococcal glomerulonephritis is explained by various theories:
– The most frequently cited mechanism is the immune complex deposition antibody-antigen in the capillaries of the glomerular basement membrane,
– Antibody formation would cause alterations in host proteins or glomerular antigens.
– Cross-reactions between glomeruli and streptococci nephritogenic exist.
– A direct toxic effect of toxins or products of streptococcal glomerular basement membranes on may intervene.
– The persistence of latent forms (form L) after initial episode was also invoked.
But none of these assumptions is not enough in itself to explain the pathogenesis of post-streptococcal glomerulonephritis. These examples give an idea of the complexity of the pathophysiology of streptococcal infections.
V – PATHOGENICITY:
A – Streptococcus pyogenes (group A):
The pathology is very varied and complex pathophysiology; we can distinguish arbitrarily:
– Local and regional events:
ENT:
-angines erythematous or erythematous pultaceous
– Abscess peritonsillar abscess, cervical adenitis, adénophlegmons
– Rhinitis, sinusitis, suppurative otitis, mastoiditis
Skin:
– Erysipelas, impetigo
– Cellulitis, necrotizing fasciitis, myonecrosis
– Secondary infections of wounds and burns, ulcers
– Vulvovaginitis, anites, repetition
– Erythema nodosum
– General events
– Early: scarlet fever, septicemia, endocarditis (rare), joint suppurative locations, pleuropulmonary, meningeal … the “toxic shock syndroms” like have been reported.
– Post-streptococcal: rheumatic fever with or without carditis, glomerulonephritis, chorea.
– Streptococci group C and G have a similar pathogenicity Group A. The post-streptococcal complications are rare.
B – Streptococcus agalactiae (group B):
– Perinatal Infections:
At the time of delivery 1-2% of children are colonized or during labor (ascending infection) or during childbirth, but only 1 in 10 children will infection.
The child may have: severe early onset occurring before the 10th day of life with respiratory distress, sepsis and meningitis sometimes. a late-appearing after the 10th day, often meningitis.
– Other infections that can be observed in adults:
– Osteo-arthritis,
– Urinary tract infections, genital, skin,
– Pleuropneumopathies,
– Septicemia, endocarditis, meningitis.
C – enterococci, streptococci and group D streptococci nongroupables called “viridans”
– Bacteremia and septicemia without pyogenic locations (various species including E. faecalis)
– Endocarditis: some species are primarily involved (Table IV) including S. sanguis, S. mitis, S. mutans, S. bovis (the latter species is often found associated with colic tumors).
– Urinary tract infections (enterococci, E. faecalis mainly).
– Dental caries (S. mutans, S. salivarius, S. sanguis, S. milleri …)
D – Other streptococci:
Different serogroups can be found in septicemia, endocarditis, meningitis (particularly S. suis isolated in meningitis in butchers).
VI – BACTERIOLOGICAL CHARACTERS:
A – Body type:
Streptococci and enterococci are in the form of Gram-positive cocci. The size of each element is less than 2 microns;it varies with the species.
Cocci are round or oval, the major axis is then in the direction of the chain.
If suffering (antibiotics, deficient mutants) of pseudobacillaires or monstrous forms can be observed, they may resent the Gram. The elements are grouped into chains shorter or longer (2 to over 50 cocci); the division taking place perpendicularly to the axis of the chain. The elements are often close * in diplococci in the chain.
They are motionless (except for some enterococci: E casseliflavus, E. gallinarum.).
A capsule can be observed in some species.
B – Cropping characters:
1. Culture conditions:
– An enhanced atmospheric CO ^ favors primocultures.
– The optimum temperature is 37 ° C, but Enterococci also grow at 45 ° C.
– The optimum pH is 7.3. Enterococci can grow in broth at pH up to 9.6. An acidic pH is detrimental to the growth of most Streptococci indeed occurs secondary acidification hence the value of the buffered medium Todd – Hewitt.
2. Appearance of colonies:
Almost all species thrive on rich agar media types
Columbia.
After 24-48 hours of culture, colonies of streptococci group A, C and G have a diameter of 0.5 mm; they are transparent, translucent dome (S).
Those of group B are wider (S), sometimes yellow-orange pigmented anaerobic.
Those in group D (enterococci) are often 0.5-1 mm wide, more opaque and often whitish may resemble staphylococcal colonies. Those of nongroupables species have varying sizes ranging from 0.1 to 0.5 mm were mucoid and shiny aspect, they are sometimes translucent.
Note that streptococci of groups A, C and G can give small colonies “minutes”, as streptococci group F.
3. Hemolysis:
The study of hemolysis around colonies on agar with 5% blood (sheep or horse) provides an initial diagnostic orientation.
– Description
We distinguish:
– Hemolysis was: Incomplete middle with greening;
– Hemolysis P: total with clarification of the agar around the colonies (diameter 3-4 mm). Hemolysis observed under aerobic conditions is due to the action of streptolysin S. This hemolysis is sharp in 24 to 48 hours, sometimes after staying at 4 ° C. Beta hemolysis hemolysis roundel with total distance of the colony and intact red blood cells in contact with the colony is sometimes observed.
– The absence of hemolysis (y).
– Influençants Factors
– Incubation atmosphere: the anaerobic promotes beta hemolysis of some streptococci
– The composition of the medium: glucose prevents the occurrence of hemolysis on blood agar cool with group A streptococci, character used for diagnostic purposes. Sodium nucleinate by accentuates against hemolysis:
– The thickness of the medium also plays a role in the visualization of hemolysis.
– Camp-test
By bringing streptococcal strain B (producing an extracellular protein called Camp-factor) and Staphylococcus aureus producing beta-hemolysin, there is at the meeting point of the two substances complete hemolysis area with a scaly appearance.
4. Selective media:
Many products containing streptococci are polymicrobial, it is useful to resort to selective media. These environments sometimes help towards a diagnostic group or species (hostile environments for groups D for example).
There is selective enrichment and isolation media.
– Medium with sodium azide (inhibits Gram -) and crystal violet (inhibits staphylococci); two media are used for research of enterococci in water: mid Rothe and mid Litsky. Todd-Hewitt medium modified to isolate B streptococci, ac environments. nalidixic + gentamicin or polymyxin crystal violet.
C – Presumptive diagnosis:
Five combined characters allow préidentification with an interesting approximation (Table V), they are:
1. Hemolysis:
or whose appearance has been described above pa
2. The test bile esculin:
The middle “bile esculin” contains 40% of bile. It must not be confused with the medium to esculin, which must not be used as presumptive test. Culture and blackening of the bile esculin medium is very specific group streptococci D. Among the viridans streptococci, positive bile esculin strains can be observed with Streptococcus mutans.
3. The broth with 6.5% NaCl:
NaCl tolerance test distinguishes enterococci from other streptococci group D. But it is not very specific since about 80% of group B streptococci show that character.
4. The sensitivity to bacitracin:
This test has been criticized because it is a poorly standardized test: the burden of disks is not always specified by the manufacturers; the inoculum density varies; the diameter of the inhibition zone considered significant, is not always the same. Maxted, which describes this test did not define the diameter of the inhibition zone.
If we accept any zone of inhibition whatever the diameter, almost all of Group A streptococci are sensitive to bacitracin.
5. The hydrolysis of sodium hippurate:
Almost every group B streptococci hydrolyze sodium hippurate.
But this character is found with some group D streptococci and some Streptococcus viridans.
It should be noted about these presumptive tests, that all of Listeria gives a positive reaction on the bile esculin medium and that two thirds of the strains of Listeria hydrolyze hippurate. The catalase is therefore important for the identification of a Streptococcus.
D – Definitive diagnosis:
The accurate identification of Streptococcus based on the study of its antigenic, and its classification in Lancefield groups. For species lacking group antigen identification based solely on the study of physiological and metabolic characteristics.
1. Structure and antigenic séroïogique classification:
a / structural antigens:
Their location is shown on the diagram of a strep-enterococcus “ideal” (Figure 1)
a) capsular antigens:
Different classes of antigens can be distinguished according to their composition:
– Hyaluronic acid: group A streptococci (S. pyogenes), and some streptococci group C (S. equi and S. zooepidemicus).
– type of polysaccharides and proteins specific for group B streptococci
– Dextrans found in some representatives of the group D (S. bovis I) or nongroupables (S. sanguis, S. mutans) or levans (S. salivarius).
b) Antigens related to the wall:
The group antigens allowed Lancefield classification, they are:
– Or polysaccharide: polysaccharide C ABCEFGHKLM-OP RSTUV groups.
– Is based teichoic acids: D and N. groups
The group antigens have been particularly well studied for A and C: Polymer rhamnose-N-acétylgIucosamine with variants and for Group B: rhamnose-N-acétylgIucosamine-galactose.
For group D, the group of antigens may not be located in the wall, but would be present in the cytoplasmic membrane or the cytoplasm.
Type antigens are often outermost position as group antigens; they are located in the outer wall layer for group A;they are
– Or proteinaceous: M proteins (related to pili), R, T sometimes associated lipoteichoic acid,
– Is such polysaccharide eg group D streptococci and some nongroupables (S. mutans).
In depth found an inner layer which corresponds to mucopeptide or peptidoglycan (chains of N-acétylgiucosamine acid N-acetylmuramic connected by tetrapeptides).
c) cytoplasmic antigens:
The cytoplasm contains a nucleoprotein complex; the teichoic acids of the D groups in free form or bound to lipids, or to what level or at the level of the cytoplasmic membrane.
Special cases
Group A streptococci:
The structural antigens have been particularly well studied (Figure 1). Among the antigens of interest in epidemiology and pathophysiology include:
– M proteins that confer
. a resistance to phagocytosis
. a type specificity (over 75 types), some related to the disease (Table VI).
Knowledge of the chemical properties of M proteins, their role and their place in a vaccine perspective has recently increased (Fischetti).
– T proteins that may be common to several types M. Moreover types M may have several types T.
-The Serum opacity factor (SOF) was found in 16 kinds M.
The antigenic typing of Streptococcus therefore includes Type M, Type T and the SOF type.
Streptococcus Group B:
Serotyping based on knowledge of the constituent protein and polysaccharide antigens, as shown in Table borrowed Geslin (Table VII); this serotype has been proposed international nomenclature: type would become the type / c; and new types have been proposed: type IV and NT1 including …
This serotype was an epidemiological and prognostic. Thus, in newborns type 1 cause rapid neonatal infection with high mortality, while type III infections cause delayed with lower mortality.
b / extracellular antigens:
Some streptococci produce extracellular substances some of which are antigenic; they were particularly studied for the group A streptococcus (Figure 2).
Among the extra-cellular antigens include:
– The erythrogenic toxin responsible for scarlet fever rash observed in and produced by lysogenic strains
– Streptolysin 0 (oxygen labile)
– DNase under 4 antigenic forms: A, B, C and D.
– The hyaluronidase, streptokinase, diphosphopyridine nucleotidase …
2. Study of the physiological and metabolic characteristics:
It identifies species lacking group antigens. It also allows in certain serogroups recognize different species.
a / The characters used are:
– physiological characters with study
– Growth at 10 ° C and 45 ° C in saline medium or at pH 9.6 in the presence of antibiotics or antibacterial
– The heating resistor
– The reduction of the tetrazolium or tellurite
* Biochemical characters, studying the metabolism:
* Carbohydrate
.the attack of certain sugars help in identification. This is a fermentative metabolism (homofermentatif); the final main product of the attack of glucose being D-lactic acid with or without formation of acetoin (VP); sugars used are especially lactose, mannitol, sorbitol; hydrolysis of esculin and starch can be desired.
. production glucans (dextran or levans) is sought on hypersaccharosé environment.
* Protein with search gelatin hydrolysis, arginine.
* Search of some enzymes is practiced: galactosidase, DNAse etc.
b / Subdivision of groups C and D:
The study of these characters the opportunity to have diagnoses of species or biotype within certain serogroups as:
. Group C: with 4 species (Table VIII)
.Group D gender Enterococcus or not (Table IX).
The species E. faecalis may itself be divided into three subspecies:
E. faecalis var. zymogens has a beta hemolysis, E. faecalis var. liquefaciens liquefies gelatin and E. faecalis var.faecalis has neither cited characters.
Other Enterococcus have been described: E. gallinarum, E. casseliflavus (both mobile), E. malodorus, E. hirae, E. mundtii (the latter two pigmented yellow as E. casseliflavus).
c / Classification streptococci devoid of group antigen or viridans streptococci (oral streptococci)
Streptococci devoid of group antigen are usually called viridans although some of them are not hemolytic. They are also called nongroupables but at grouping tests by the method of
Lancefield ring is sometimes observed with the group H, K and E.
These streptococci are responsible for about half of the cases of endocarditis slow.
The characters that identify them are shown in Table X. There are other species of oral streptococci including S.anginosus, S. constellatus, S. intermedius, S.oralis recently S. vestibularis (Coykindall, Schleifer).
The appearance of colonies on an agar medium at 5% sucrose can recognize strains that produce dextrans or levans, usefulness for diagnosis.
The use of a broth of 5% sucrose is interesting for diagnosis of S. sanguis causing gelling of the medium and S.mutans which forms a deposit that adheres to the walls and bottom of the tube.
Nongroupables of streptococci, one must bring the deficient streptococci, also referred to as: thiol-dependent, dependent on vitamin B6 and pyridoxal. These strains are often grown in broth while they are unable to grow on agar medium. It is usually possible to obtain an agar culture by practicing satellitism test. The deficient streptococcus strain is seeded by floating on a blood agar plate, in the manner of susceptibility testing. This box is then carried out a groove with a culture of Staphylococcus aureus. The defective streptococcus grows under culture of S. aureuswhich he uses the catabolism of products it can not synthesize itself. Recent taxonomic studies propose to distinguish two species in deficient streptococci: S. defectius and S. adjacens.
VII – DIRECT DIAGNOSIS:
A – Collection and cultures:
1. Blood cultures:
They are used in a clinical setting of sepsis or endocarditis. One must practice between 6 and 10 blood cultures over 48 hours using 2 types of bottles: aerobic and anaerobic (brain heart, Schaedier). The use of rich media for the cultivation of streptococci impaired (enriched with thiol groups) is sometimes useful. Subcultures should be made after research disorder or microcolonies before any agitation on environments rich in blood, blood boiled anaerobic CO2 atmosphere. If morphology is suggestive, can be grown Streptococcus deficient satellitism a streak staphylococcus and special media. Nearly all species of streptococci or enterococci can be retrieved. The interpretation of blood culture with a single positive blood culture containing a non-hemolytic streptococcus is tricky.
2. Cerebrospinal Fluid – medulla:
Group B strep is usually isolated from the newborn. The liquid is in order purulent, but culture can sometimes be positive in the absence of cellular reaction, especially in newborns. Seeding on blood agar under CO ^ promotes growth. Isolation in CSF of a non gangable enterococcus or streptococcus must be interpreted with caution outside a particular context, or repeated isolations, especially if direct examination is negative.
3. Urine:
Urinary tract infections streptococci groups D and B are not exceptional. Enterococci are common contaminants of urine, as she has the quantitative bacteriology particular interest; isolation requires the use of a blood agar.
4. Samples throat:
The samples should be taken with a tongue depressor, under visual control. The swab is effected by contacting the tonsils, pharyngeal mucosa and / or purulent areas or cryptic.
If the swab can not be placed in a transport medium or survival, it must be moved quickly after being moistened beforehand with saline. Research is focusing primarily beta-hemolytic streptococci group A. The identification of enterococci or streptococci nongroupables is normal, these bacteria form part of the commensal flora. Enrichment media can be used in parallel with the selective isolation media.
5. Skin samples:
Mark of beta-hemolytic streptococci not only, but also C and G to be systematic in skin diseases in general, especially erysipelas, either by simple swab or swab at the biopsy port.
All streptococci can be found in the pus or purulent collections, but enterococci and streptococci nongroupables are normal skin flora elements and frequently contaminate local levies.
6. Genital samples:
P-haemolytic streptococci A and B should be sought.
7. Device samples:
They are mostly performed in newborns, in assessing the neonatal colonization. Systematic reviews involve looking streptococcus B:
– Amniotic smears of gastric fluid smears,
– Placental smears,
– Superficial samples: anus, eyes, mouth, skin …
8. Other charges:
It may be necessary to seek streptococci in:
– Heart valves during post-endocarditis interventions or autopsies,
– The water feed to detect fecal contamination (enterococci).
B – Diagnostic Approach:
Direct examination of some samples: pus, puncture fluids, CSF can … viewing cocci in chains to be suggestive of streptococci. Also this morphology observed on crops, and typical colonies, together with the observation of haemolysis type allows an orientation of the diagnosis.
Schematically:
1. If one is in front of beta-hemolytic colonies, proceed immediately to a grouping in the Lancefield system by successively:
– A mining group antigen: not by the conventional technique of Lancefield (HC1 extraction), or formamide or autoclave (reserved for certain groups D), but rather by such chemical technique extraction nitrous, or by enzymatic extraction (pronase B, or enzyme of Streptomyces albus, or combination of this enzyme with lysozyme: at 37 ° C or 45 ° C for 30 to 120 minutes according to manufacturer’s recommendations).
– A demonstration of the group antigen, rarely present by capillary precipitation test or immunoelectrophoresis against, but rather by agglutination reaction by bringing the extract with particles coated with antibodies antigroupes A, B, C, D, F and G is fixed on the Staphylococcus aureus protein A carrier (coagglutination) or on the latex particles.
2. If the settlements are not beta-hemolytic, can be in the presence of incomplete hemolysis only giving beta hemolysis in the presence of staphylococcal toxin (Camp test for group B).
Usually alpha-hemolytic colonies (yiridans) or non-haemolytic streptococci match D group or nongroupables. We can then make a referral gallery (Table IV) or directly in a line to get to the gallery species diagnosis. Either classical galleries are used either ready-galleries (API strep …), supplemented by the study of cultural characters, the production of dextrans levans, and the search for group antigens (extraction formamide, heat) to the group D in particular, and the search of the rarest groups other than A, B, C, F, G …
C – antigenic Diagnosis:
– Immunofluorescence was advocated on direct smear for the detection of Streptococcus A and B. This technique has been little development in France.
– Looking for Group B antigens is useful for the diagnosis of neonatal infections by searching soluble antigens in CSF, serum or urine. Search extractable antigens directly on genital swabs is under consideration.
– Looking for Group A antigens can be performed directly on nasopharyngeal swab after extraction or nitrous or enzymatic reaction by agglutination (Latex or coagglutination) with quick results (10 to 30 minutes); more rarely by ELISA.
VIII – INDIRECT DIAGNOSIS:
Currently available reagents used to assay for antibodies primarily against group A streptococci; However, there are cross-reactions with other beta-hemolytic streptococci.
The main toxins and enzymes Assayable inducing antibodies, the properties of these enzymes, the principle of their dosage and normal levels are summarized in Table XI.
Comments about this serology:
– There is in every healthy individual antibody variable rate
– Thresholds considered pathological often vary depending on the kits, the manufacturers and the units adopted
– the antistreptolysin 0 totaled more after mucosal infection after skin infection. The standard rate does not exceed 100 IU / ml in children of preschool age and in adults 200 IU / ml.
Hyperlipemic sera may give false positive rate of ASO due to the presence of lipoprotein and cholesterol, treatment with dextran sulfate, overcomes this difficulty.
A significant rise in ASO peaked in 3 to 4 weeks and calls 2-4 months to get back to normal. The observation of a rising stock has more interest than the observation of a single high titre.
The antistreptodornases B (DNAses B) are more faithful witnesses of a skin infection streptococci that ASLO: they are indeed high in 89% of cases against 36% for ASLO. In the pharyngeal infections, like the ASLO ANADases are usually higher than the DNAses B. ASH rise more in the skin infections.
The most sensible choice of an association is more ASLO DNAses B leads to 98% diagnostic efficiency. The most currently used serological reactions are ASLO DNAses and B; others (ANADases, ASH and ASK) is very little used and elsewhere seem a minor interest.
Some passive agglutination by screening reactions allow the simultaneous detection of multiple antibodies, this is the case streptozyme ® The test is considered positive if the agglutination is observed to a greater or serum dilution equal to 1 / lOOème. This type of test allows rapid preliminary diagnosis but it is not always effective in detecting DNAses B.
The dosage of antibodies against group B streptococcus is not yet widely practiced. Performed on the serum of mothers, it would have the interest to predict which infants receiving a maternal protection transplacental transmission of antibodies.
Through obtaining certain streptococcal antigens purified, it was possible to achieve only as research, sérodiagnotics in a context of endocarditis (E. faecalis in particular) or Immunoprophylaxis in neonatal streptococcal infections Group B in pregnant women.
IX – TREATMENT:
A – Prevention:
– Vaccination against group B streptococci is investigated; the same against group A study using as vaccine antigen of M proteins are ongoing.
– Caries prevention by vaccination is also envisaged.
Antibiotic prophylaxis is recommended for prevention of endocarditis consecutive tooth extractions and to prevent post-streptococcal complications.
B – Healing; Sensitivity to antibiotics:
Bacteria of the Streptococcus genus have long remained susceptible to most antibiotics. The emergence in recent years of strains resistant to antibiotics traditionally used such as penicillins, macrolides and related (2% resistors for group A 6 to 18% for group B and 47% for E. faecalis), chloramphenicol and cyclins, requires careful monitoring of these resistances, both from an epidemiological perspective than curative.
1. Methods of study:
a / The conventional susceptibility testing:
It is performed using a Mueller-Hinton medium supplemented with 5% blood and an inoculum obtained by dilution of a broth culture, heavy inoculum (groups A, C, F and G), light (B and D) or intermediate (nongroupables).
Incubation for 18 hours at 37 ° C in CO2 atmosphere, is performed.
b / Determining the level of resistance to aminoglycosides:
Two techniques can be used:
– A diffusion technique with a disc containing 250 mcg to 500 pg gentamicin and streptomycin. Resistance to high level give a diameter less than 10 and 12 mm respectively, to low level, respectively upper 14 and 18 mm.
– A brain-heart agar with 5% horse serum in which a final concentration was incorporated 1 000 and 2000 mg / 1 of the aminoglycoside to be studied. A strain that develops on the environment has a high-level resistance to aminoglycoside considered.
c / Detecting tolerance:
For streptococci considered limits or resistant to penicillin, or enterococci, it may be necessary (including endocarditis) to determine the MIC and MBC in liquid medium. Strains, one can find “tolerant” to penicillin that is to say for which the MIC / MBC ratio is greater than 32. The truly resistant strains are most noticeable among nongroupables streptococci and enterococci.
A simple method of tolerance detection can be done on the box antibiogram. It is, after reading the antibiogram, to place in the zone of inhibition of penicillin a disc containing a beta-lactamase. After a further incubation of 18 hours, the growth of the bacterium in the zone of inhibition where the beta-lactamase destroyed penicillin means penicillin did not have a lethal effect on the strain.
Rapid detection of tolerance. Pase = disk penicillinase PEN = penicillin disc
2. Current Status of the sensitivity of streptococci:
Streptococci are generally sensitive to penicillins and macrolides.
They are resistant to polymyxin and often quinolones. There is a natural resistance to aminoglycosides are only inactive, but often have a synergistic action with penicillins. Generally cephalosporins are less active than penicillins.Streptococci have vis-à-vis behavior of antibiotics that differ according to species. Generally, enterococci are more resistant.
a / Group A Streptococcus:
All strains of streptococci group A are sensitive to penicillin G.
The MIC is between 0.005 mg / 1 and 0.02 mg / 1. Penicillin G is the antibiotic of choice for prophylaxis and treatment of group A streptococcal infections A.
The macrolides and related antibiotics are used in case of allergy to penicillin G. The strains resistant to these antibiotics are exceptional in France, while this resistance is common in other countries.
Cyclins have variable activity depending on the strain. The percentage of group A streptococci resistant to these antibiotics is between 20 and 30%.
b / Group B Streptococcus:
This species is slightly less sensitive to penicillin G as the group A. The MIC 50% of the strains is 0.03 mg / 1. These strains are still easily accessible to treatment with penicillins.
Related macrolides are active in the majority of cases, but about 5% of the strains were resistant to these products.
As regards the action of cyclins two populations are observed: 80% of the strains are resistant to tetracyclines; others are susceptible.
c / Streptococcus group D:
Enterococci (E. faecalis, E. faecium summer. Durans) are relatively more resistant to antibiotics. But to treat endocarditis is essential to have a bactericidal treatment.
Penicillins are less active vis-à-vis enterococci and vis-à-vis other streptococci. The MIC of penicillin G as that ampicillin is between 1 and 8 mg / 1. E. strains faecium are the most resistant.
In endocarditis, bactericidal activity was obtained by combining a high dose of penicillin with an aminoglycoside.
IJC vis-à-vis enterococci streptomycin is generally between 25 and 100 mg / 1. This low-level resistance to this antibiotic streptomycin allows to have a synergistic action with penicillin. In a number of cases, which can reach 20% with E. faecalis, there is a high level of resistance to aminosidesrexpliqué by acquiring a neighboring modifying enzyme of that detected in S. aureus (rather than a rare chromosome mutation). For these strains, the MIC of streptomycin is very high, it is still well above 1000 mg / 1. Is no longer observed synergistic activity of penicillin and streptomycin.
The combination of the penicillin with another aminoglycoside remains generally synergistic vis-à-vis these strains.However, of E. faecalis strains highly resistant to gentamicin were described. In practice, before the results of laboratory tests, the combination of penicillin and gentamicin is often preferable to conventional combination penicillin and streptomycin.
If the combination penicillin and aminoglycoside is not usable, a bactericidal treatment is often achieved by combining erythromycin and cyclin. The bactericidal action of this association on the enterococcus strain to be treated must be verified in the laboratory.
In the absence of ability to use both types of association, it remains to use a process comprising vancomycin or teicoplanin or rifampicin.
As for S. bovis its antibiotic sensitivity approaching the so-called viridans streptococci although some strains highly resistant to aminoglycosides have been observed.
d / Streptococcus viridans:
Streptococcus viridans have pathogenicity limited outside endocarditis. Their sensitivity to penicillin G is good. The MIC is between 0.06 and 0.5 mg / 1. Also, it has been proposed treatments using penicillin alone. It seems difficult to establish rigid attitudes to treatment of streptococcal endocarditis. Considering the severity of the disease, any strep strain isolated during endocarditis should be a comprehensive study of its antibiotic sensitivity, even if it belongs to a reputed sensitive species. Further research associations and synergistic bactericidal antibiotic in vitro is absolutely necessary. Indeed, in some strains of susceptible species may have unusual resistance.
3. Monitoring of treatment of endocarditis:
Laboratory tests are used to assess whether antibiotic treatment is bactericidal and suitable. These tests are:
– Research negativity blood cultures;
– The dosage of antibiotics for effective rates, but non-toxic (aminoglycosides, vancomycin, teicoplanin)
– The study of the effective ratio, serum / MIC or MBC;
– The determination of bactericidal serum (PBS). It is satisfactory if dilution at least equal to 1/16 leaves a number of bacteria surviving less than or equal to l% o seeded bacteria (standardization of this technique is still a problem).