Unit 13. Streptococci.pdf

Microbiology Unit 13 Streptococcus genus Ve más allá 1 Streptococcus spp. MICROBIOLOGICAL CHARACTERISTICS AND IDENTIFICATION  Gram-positive cocci.  Arranged in pairs, short or long chains  Facultative anaerobes  Fermentation and lactic acid production: importance in caries, Streptococcus mu...

Microbiology Unit 13 Streptococcus genus Ve más allá 1 Streptococcus spp. MICROBIOLOGICAL CHARACTERISTICS AND IDENTIFICATION  Gram-positive cocci.  Arranged in pairs, short or long chains  Facultative anaerobes  Fermentation and lactic acid production: importance in caries, Streptococcus mutans).  Growth favored by an atmosphere with 5-10% CO2 (capnophilic growth).  Growth in standard media (nonselective) such as blood agar at 37 ° C.  Some species are hemolytic.  Very heterogeneous group (normal microbiota, pathogens)  Catalase negative ⇒ difference with Staphylococcus. Fuente: Public Health Image Library (PHIL), CDC. Streptococcus spp.: CLASSIFICATION Several classification schemes. One is not enough for identification. 1. HEMOLYTIC PATTERNS:  α-hemolytic streptococci: incomplete or partial hemolysis (green color in blood agar).  β-hemolytic streptococci: complete hemolysis (transparent color in blood agar).  γ-hemolytic streptococci: no hemolysis (red color in blood agar). Streptococcus spp.: CLASSIFICATION BY HEMOLYSIS Alpha hemolysis:incomplete. greenish color Netha Hussain. 2012. Blood_agar_showing_alpha_hemolysis.JPG Disponible en: commons.wikimedia.org/wiki/File:Blood_agar_showing_alpha_hemolysis.JPG Beta hemolysis: complete. Transparent Nathan Reading from Halesowen, UK. 2011. Streptococcus pyogenes (Lancefield Group A) on Columbia Horse Blood Agar - Detail.jpg Disponible en: commons.wikimedia.org/wiki/File:Streptococcus_pyogenes_(Lancefield_Group_A)_on_Columbia_Horse_Blood_Agar_-_Detail.jpg Streptococcus spp.: ANTIGENIC STRUCTURE CLASSIFICATION 2. ANTIGENIC STRUCTURE:  Lancefield groupings (Rebecca Lancefield 1933):  They share the same antigen 'group'  A: S. pyogenes  B: S. agalactiae  D: Enterococci (now belongs to another genus)  C and G: animal Streptococci β - hemolysis  NO Lancefield antigens  Viridans streptococci group  S. pneumoniae α - hemolysis Streptococcus spp.: AGGLUTINATION The presence of these antigens allows us to perform identification tests in the laboratory: Ex: Adding of specific antibody against antigen A Slide with S. pyogenes Slide with S. agalactiae Macroscopic agglutination https://commons.wikimedia.org/wiki/File:Latex_slide_agglutination_test.jpg No agglutination Streptococcus spp.: CLASSIFICATION 1. S. pyogenes (β-hemolytic, group A) 2. S. agalactiae (β-hemolytic, group B) 3. S. pneumoniae (α-hemolytic) 4. Viridans streptococci (α-hemolytic)  Streptococcus mutans group  Streptococcus mitis (S. oralis group)  Streptococcus salivarus … 5. Enterococcus spp. (nonhemolytic, group D, now belongs to another genus) Viridans streptcococci Viridans streptococci  Gram-positive cocci Habitat: oropharyngeal cavity.  Colonize hard and soft surfaces.  In dentistry associated with:  Plaque formation and caries production.  Gingivitis, periapical abscesses, pulpitis etc.  Outside the oral cavity:  Endocarditis: dental instrumentation!  In neutropenic patients serious infections  They are not clear pathogens in other infectious diseases (opportunistic)  Encompass many species sometimes difficult to distinguish and to classify. Viridans streptococci: CLASSIFICATION  Streptococcus mutans group  S. mutans  S. sobrinus  S. cricetus  S. ratti  Streptococcus mitis group (oralis group)  S. oralis  S. mitis  S. sanguinis (previously S. sanguis)  Others  Streptococcus anginosus group  S. anginosus, S. intermedius, S. constellatus  Streptococcus salivarius group  S. salivarius, S. vestibularis Streptococcus mutans GROUP  No capsule  No "Lancefield“ antigens  Great mucous layer with glucans and glycosyltransferases that are secreted outside the cell and involved in bacterial aggregation phenomena → help in the formation of plaque.  Wall proteins involved in binding and adhesion  Sucrose metabolism, producing lactate fermentation with acid production (lactic acid).  Cariogenic microorganisms, especially S. mutans. Streptococcus mutans GROUP Streptococcus mutans  The most common species of the group.  Present in 70-90% of the population. In people with active caries the presence of S. mutans increases significantly.  Cariogenicity factors:  Synthesis of an extracellular glucan type polysaccharide (provided by the presence of sugars in diet, especially sucrose)  Acidic, aciduric and acidophilic power.  Adhesion by adhesins and cell wall associated proteins. Streptococcus mutans Acidic Acidophilic Aciduric Acid production Growth at low pH Acidifies the acid pH Streptococcus mitis GROUP  S. oralis, S. mitis, S. sanguinis  Non capsulated.  Alpha-hemolytic.  Non growth at pH= 5, non acidophilic.  Generally do not synthesize (or not as much amount as S. mutans) extra and intracellular polysaccharides involved in the production of dental plaque.  Poor cariogenic capacity.  Isolated in oropharynx, skin, female genital tract and intestines.  Main microorganisms involved in subacute endocarditis: S. mitis and S. sanguinis (previously S. sanguis) TREATMENT FOR VIRIDANS STREPTOCOCCI  Generally sensitive to penicillins, macrolides, lincosamides, aminoglycosides and glycopeptides.  Directed treatment after antibiogram results because of the recent increase of penicillin and macrolides resistance.  In dental plaque and caries: dental cleaning, reducing bacterial load and polysaccharide matrix. Streptococcus pneumoniae Streptococcus pneumoniae: PNEUMOCOCCUS  Gram-positive cocci in pairs and chains  Alpha-hemolytic, draughtsman-shaped (dimpled appearance) colonies  Sensitive to optochin  Soluble in the presence of bile salts  Some strains have the ability to be surrounded by a polysaccharide capsule (mucoid colony) DIFFERENTIAL DIAGNOSIS Streptococcus pneumoniae Streptococcus pneumoniae: Optochin test Copacopac. 2012. A-hämolysierende Streptokokken.jpg Disponible en: commons.wikimedia.org/wiki/File:Ah%C3%A4molysierende_Streptokokken.jpg?uselang=es Streptococcus pneumoniae INFECTIONS  Important RESPIRATORY and SYSTEMIC pathogen  No dental implication  It can appears as a transient colonizer of the oropharynx mucosa Streptococcus pneumoniae INFECTIONS Gram positive cocci, chain arrangement, α-hemolytic, transient colonizer of the oral cavity, no member of the normal microbiota Similiar to Streptococcus viridans group, so DIFFERENTIAL DIAGNOSIS IS NECESSARY: Streptococcus pneumoniae Streptococcus viridans BILE SOLUBILITY + OPTOCHIN SENSITIVITY S R α-HEMOLYSIS + + Streptococcus pneumoniae INFECTIONS 1st cause of bacterial pneumonia Bacterial conjunctivitis Common cause of respiratory focused bacteremia 1st cause of bacterial otitis and sinusitis Pneumococcus Not important in dentistry After meningococci, a major cause of bacterial meningitis Streptococcus pyogenes Streptococcus pyogenes  Gram-positive cocci in chains  β-hemolytic white colonies  GROUP "A" of Lancefield  Epidemiology:  Not normal microbiota  Person-person transmission (coughing, hands, fomites)  Adults and children can be colonized (healthy carriers)  Colonization depends on the ecological niche left by viridans streptococci PATHOGENICITY Streptococcus pyogenes VIRULENCE FACTORS  STRUCTURE:  Teichoic acid, capsule (some) or slime.  M protein:  Included within the peptidoglycan.  Major virulence antigen. one of the most extensively studied bacterial virulence factors. The best-known property of M protein is its ability to inhibit phagocytosis in non-immune humans  Lack of M protein: non-virulent strain.  Adherence to tissues  Antigenic similarity with proteins from heart and kidney: autoimmune diseases. PATHOGENICITY Streptococcus pyogenes VIRULENCE FACTORS TOXINS:  Erythrogenic toxin (nowadays called pyrogenic exotoxin): Superantigen. Rash of Scarlet Fever.  Streptolysin O: hemolysin (O2-Sensitive)  Produces hemolysis in anaerobiosis.  Antigenic: antibodies anti-streptolysin O (ASLO). Ag-Ab complexes damage tissues (heart, joint, kidney). PATHOGENICITY Streptococcus pyogenes VIRULENCE FACTORS  ENZYMES:  Streptokinase: dissolves the fibrin clot facilitating the spreading of the bacteria (therapeutic use in strokes)  Hyaluronidase: breaks down connective tissue.  DNAse (skin infection)  Protease ... PATHOLOGIES Streptococcus pyogenes S. pyogenes DISEASES SUPPURATIVE INFECTIONS NONSUPPURATIVE DISEASES: IMMUNOLOGICAL PATHOLOGIES Streptococcus pyogenes Suppurative infections A-RESPIRATORY:  Pharyngitis and pharyngoamigdalitis (tonsilitis)  occasionally peritonsillar abscess  scarlet fever (occasionally)  Sinusitis  OTITIS B-SKIN:  Impetigo: (stratum corneum)  Erysipelas: superficial cellulitis (dermis) C-SOFT TISSUES:  Cellulitis (skin and deeper subcutaneous tissues)  Fasciitis - necrotizing myositis D-SEPSIS: Postpartum sepsis, cellulitis, etc Streptococcus pyogenes Nonsuppurative diseases A- Acute rheumatic fever:  CROSS REACTIVITY WITH "M" PROTEIN  10-15 days POST-PHARYNGITIS (never after skin infection)  Syndrome characterized by (Jones criteria): • carditis • migratory polyarthritis • Sydenham chorea (St. Vitus dance) • erythema marginatum • subcutaneous nodules • evidence of streptococcal infection B- Acute glomerulonephritis:  AUTOIMMUNE DISEASE  AFTER PHARYNGITIS OR SKIN INFECTION Streptococcus pyogenes TREATMENT  EXTREMELY SENSITIVE TO PENICILLIN  MILD INFECTIONS:  ORAL PENICILLIN or amoxicillin  Non β-lactamase producing (NO clavulanic acid)  SEVERE INFECTIONS:  I.V. PENICILLIN (+ clindamycin)  Cellulitis - Fasciitis: SURGERY + antibiotic ALLERGY TO β -lactams:  macrolides (Erythromycin) (note: resistance 25-30%) in mild infections  vancomycin (in hospital) in severe infections  SPECIAL CASES:  Acute rheumatic fever prophylaxis: Penicillin THANKS FOR YOUR KIND ATTENTION! QUESTIONS PLEASE? Ve más allá © Copyright Universidad Europea. Todos los derechos reservados