Streptococcus spp. and Enterococcus spp.

• Streptococcus spp.

  Family Streptococcaceae, Catalase negative, Gram positive cocci in pairs and chains, Facultative anaerobes, Aerotolerant anaerobes, Capnophilic, Can ferment glucose but no gas, Colonies are small [pinpoint]and transparent
• Streptococci and Enterococci


  • No bubble formation (unlike Staphylococci and Micrococci which have bubble formation)
• Streptococci and Enterococci


  • Appear more elongated compared to Staphylococci's cocci which are bilog na bilog
• Streptococci and Enterococci


  • Form chains when grown in broth cultures
• Classification of Streptococcus spp.

  • Based on colonial morphology and hemolytic reactions on blood agar
  • Based on serologic specificity of the cell wall group-specific substance
• Beta-hemolytic pattern


  Clear surrounding, complete lysis of RBCs
• Alpha-hemolytic pattern


  Greenish discoloration due to partial hemolysis of RBCs
• Non-hemolytic pattern


  No change, no RBCs lysed
• Lancefield Classification


  Based on the C carbohydrate (polysaccharide) in the cell wall
• Lancefield Groups

  • Group A: Rhamnose-N-acetylglucosamine
  • Group B: Rhamnose-glucosamine polysaccharide
  • Group C: Rhamnose-N-acetylgalactosamine
  • Group D: Glycerol teichoic acid containing D-alanine and glucose
  • Group F: Glucopyranosyl-N-acetylgalactosamine
• Beta hemolytic pattern


  Not always demonstrated by Groups A, B, and C streptococci, but they usually do
• Alpha hemolytic pattern


  Demonstrated by S. pneumoniae and Viridans streptococci
• Non-hemolytic pattern

  Demonstrated by Group D streptococci and Enterococcus spp.

  
• The Group Antigens are classified into certain hemolysis types, but they do not demonstrate such types all the time
• According to the book of Mahon, the antigens are acid labile except for antigen B which is acid stable
• M Protein


  Encoded by the emm genes, resists phagocytosis and adheres the bacterial cell to mucosal cells, over 150 serotypes
• Protein F and Lipoteichoic Acid


  Adherence to epithelial cells
• Hyaluronic Acid Capsule


  Impedes phagocytosis, most noticeable in very young cultures
• Streptolysin O (SLO) and Streptolysin S


  Exotoxins that damage intact RBCs, SLO can initiate a highly immune response
• DNase A, B, C, and D


  Potent protease that interferes with phagocytosis, spreads streptococci in tissue by liquefying pus, immunogenic (most common is DNase B)
• Streptokinase or Fibrinolysin


  Lyses fibrin clots through the action on plasminogen, allows bacteria to escape from blood clots, immunogenic but not specific to GAS
• Hyaluronidase


  Spreading factor, enzyme that solubilizes the ground substance of mammalian connective tissues
• Streptococcal Pyrogenic Exotoxins


  Erythrogenic toxins that cause a red spreading rash, referred to as scarlet fever (SpeA, SpeB, SpeC, SpeF)
• Streptococcus pyogenes Infections

  • Bacterial pharyngitis (strep throat)
  • Pyodermal infections (impetigo, cellulitis, erysipelas, wound infection, arthritis, scarlet fever)
  • Necrotizing fasciitis (type 2)
  • Streptococcal toxic shock syndrome
  • Poststreptococcal sequelae (rheumatic fever, acute glomerulonephritis)
• Streptococcus agalactiae Capsule


  Resists phagocytosis but is ineffective after opsonization, component is sialic acid (unlike S. pyogenes which has hyaluronic acid)
• Streptococcus agalactiae Virulence Factors

  Hemolysin, CAMP factor, neuraminidase, DNase, hyaluronidase, and protease, but do not cause infection
• Streptococcus agalactiae Infections

  • Invasive disease of newborns (vertical transmission, colonization in vagina and rectal area)
• Specimen Collection for S. pyogenes

  1. Throat swab, pus, cerebrospinal fluid or other sterile body fluid, or blood

  2. Swab: tongue should be depressed and swab rubbed over posterior pharynx and tonsillar areas

  3. Exudate: touched with swab

  4. Avoid tongue and uvula
• Specimen Collection for S. agalactiae

  1. Vaginal and rectal material with swabs between 35 and 37 weeks of gestation

  2. Transport medium: Todd-Hewitt broth (10 microgram/mL colistin) and Lim broth (15 microgram/mL nalidixic acid)
• Direct Microscopic Examination

  Gram positive cocci, round or oval-shaped, occasionally forming elongated cells
• Culture

  1. BAP, BAP containing sulfamethoxazole (SMZ) or colistin and polymixin B

  2. 18 to 24 hours of incubation at 35°C to 37°C aerobically or anaerobically
• S. pyogenes Colonies


  Small, transparent, and smooth with a well-defined area of beta-hemolysis
• S. agalactiae Colonies


  Grayish white mucoid colonies surrounded by a small zone of beta-hemolysis, orange or red pigment in StrepB Carrot Broth after 6 hours incubation
• Microscopic Examination

  Gram positive cocci with some short chains
• Catalase Test

  Streptococci and Enterococci have no or few bubble formation, unlike Staphylococci and Micrococci which have bubble formation
• Bacitracin Test (Taxo A)


  Presence of zone of inhibition around the disk indicates sensitivity (S. pyogenes), no zone indicates resistance (other beta-hemolytic streptococci)
• PYR Test

  Bright red color indicates positive (S. pyogenes), no color change or orange color indicates negative (other beta-hemolytic streptococci)
• Hippurate Hydrolysis Test

  Deep purple color indicates positive (S. agalactiae), colorless or slightly yellow pink color indicates negative (other beta-hemolytic streptococci)
• CAMP Test

  Enhanced hemolysis indicated by an arrowhead-shaped zone at the juncture of the two organisms indicates positive (S. agalactiae), no enhancement of hemolysis indicates negative (other beta-hemolytic streptococci)
• Streptococcus pneumoniae


  Member of the S. mitis group, does not have C carbohydrate so no Lancefield classification, cell wall has C substance that reacts with CRP to form precipitate