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• Streptococcus genus


  • 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

  
• Several classification schemes. One is not enough for identification.
• 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)
• Lancefield groupings


  • A: S. pyogenes
  • B: S. agalactiae
  • D: Enterococci (now belongs to another genus)
  • C and G: animal Streptococci
  • No Lancefield antigens: Viridans streptococci group, S. pneumoniae
• Agglutination


  1. Adding of specific antibody against antigen A

  2. Macroscopic agglutination

  3. No agglutination
• Streptococcus spp. classification


  • S. pyogenes (-hemolytic, group A)
  • S. agalactiae (-hemolytic, group B)
  • S. pneumoniae (-hemolytic)
  • Viridans streptococci (-hemolytic): Streptococcus mutans group, Streptococcus mitis (S. oralis group), Streptococcus salivarus
  • Enterococcus spp. (nonhemolytic, group D, now belongs to another genus)

  
• Viridans streptococci


  • Gram-positive cocci
  • Habitat: oropharyngeal cavity
  • Colonize hard and soft surfaces
  • In dentistry associated with plaque formation, caries, gingivitis, periapical abscesses, pulpitis
  • Outside the oral cavity: endocarditis, serious infections in neutropenic patients
  • Encompass many species sometimes difficult to distinguish and to classify
• Viridans streptococci groups


  • Streptococcus mutans group: S. mutans, S. sobrinus, S. cricetus, S. ratti
  • Streptococcus mitis group (oralis group): S. oralis, S. mitis, S. sanguinis
  • 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 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
  • Present in 70-90% of the population, increased presence in people with active caries

  
• Streptococcus mutans cariogenicity factors

  • Synthesis of an extracellular glucan type polysaccharide
  • Acidic, aciduric and acidophilic power
  • Adhesion by adhesins and cell wall associated proteins

  
• Streptococcus mitis group


  • 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

  
• 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


  • Gram-positive cocci in pairs and chains
  • Alpha-hemolytic, draughtsman-shaped colonies (dimpled appearance)
  • Sensitive to optochin
  • Soluble in the presence of bile salts
  • Some strains have the ability to be surrounded by a polysaccharide capsule (mucoid colony)

  
• Streptococcus pneumoniae is an important respiratory and systemic pathogen, but has no dental implication and can appear as a transient colonizer of the oropharynx mucosa

  
• Streptococcus pneumoniae


  1st cause of bacterial pneumonia, 1st cause of bacterial otitis and sinusitis, common cause of respiratory focused bacteremia, after meningococci, a major cause of bacterial meningitis

  
• Streptococcus pneumoniae is not important in dentistry
• Streptococcus pyogenes


  • Gram-positive cocci in chains
  • β-hemolytic white colonies
  • Group "A" of Lancefield
  • 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

  
• Streptococcus pyogenes structure


  • Teichoic acid, capsule (some) or slime
  • M protein: included within the peptidoglycan, major virulence antigen, lack of M protein: non-virulent strain, adherence to tissues, antigenic similarity with proteins from heart and kidney: autoimmune diseases

  
• Streptococcus pyogenes virulence factors

  • Toxins: Erythrogenic toxin (superantigen, rash of Scarlet Fever), Streptolysin O (hemolysin, O2-sensitive, antigenic, Ag-Ab complexes damage tissues)
  • Enzymes: Streptokinase, Hyaluronidase, DNAse, Protease

  
• Streptococcus pyogenes diseases


  • Suppurative infections: Respiratory (pharyngitis, pharyngoamigdalitis, sinusitis, otitis), Skin (impetigo, erysipelas), Soft tissues (cellulitis, fasciitis - necrotizing myositis), Sepsis
  • Nonsuppurative diseases: Immunological pathologies (Acute rheumatic fever, Acute glomerulonephritis)

  
• Streptococcus pyogenes treatment


  • Extremely sensitive to penicillin
  • Mild infections: oral penicillin or amoxicillin (non β-lactamase producing)
  • Severe infections: IV penicillin (+ clindamycin), cellulitis - fasciitis: surgery + antibiotic
  • Allergy to β-lactams: macrolides (erythromycin), vancomycin (in hospital)
  • Acute rheumatic fever prophylaxis: penicillin