Streptococci

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Streptococci
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• Streptococcus
• Gram positive spherical or ovoid cells, arranged
  in chains or pairs
• Non spore forming,
• Non-motile
• Some species form capsules of polysaccharides or
  hyaluronic acid
• Small, non pigmented colonies
• Most streptococci are facultative anaerobes, and
  some are obligate (strict) anaerobes.
• Do not form catalase

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Freshly isolated Streptococcus
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Classification

• Based on their hemolytic properties on blood agar
  
• Lancefield Grouping
• species-specific CHO cell wall antigens
• groups designated A-H, K-V
• some not groupable (e.g., Streptococcus
  pneumoniae and viridians streptococci).

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Human Streptococcal Pathogens

• S. pyogenes
• S. agalactiae
• Viridans streptococci
• S. pneumoniae
• Enterococcus faecalis

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Streptococcus pyogenesPyogenes means pus
producing

• Inhabits throat, nasopharynx, occasionally skin
• It is the main human pathogen associated with
  local or systemic invasion and poststreptococcal
  immunologic disorder.
• Gram positive cocci in chains
• Lancefield Serological Group A
• Beta Hemolytic on blood agar

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Clinical disease

• pharyngitis (streptococcal sore throat),
  osteomyelitis, endocarditis, septic arthritis,
  and meningitis.
• It may also infect the skin, causing erysipelas,
  impetigo, or cellulitis.
• two autoimmune diseases, rheumatic fever and
  acute glomerulonephritis.
• Other toxigenic S. pyogenes infections may lead
  to streptococcal
• toxic shock syndrome, scarlet fever.

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• Laboratory diagnosis
• 1-Blood agar very small, white to grey colonies
  approximately 1mm in diameter surrounded by a
  zone of beta hemolysis.
• 2- Sensitive to bacitracin.
• 3-Serological test streptolysin O stimulate
  Anti- streptolysin O (ASO) antibody ASO test) is
  indicative of previous pharyngeal infection.

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2-Group B streptococci (GBS or Streptococcus
agalactiae)

• Often found in the upper respiratory tract and
  genitourinary tract of healthy adults
• Gram-positive cocci
• Typically form short chains in clinical specimens
  and longer chains in laboratory media.
• A small zone of beta hemolysis on Blood agar,
  although some strains are non-hemolytic.
• Resist to bacitracin.

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Streptococcus Pneumonia

• Gram positive, They typically appear as a
  diplococcus
• Alpha hemolytic,
• Not of lancefield serotype
• Often part of normal flora of respiratory track
  and becomes infective once hosts resistance is
  lowered. Classified as an endogenous infection.
  

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Strep Pneumonia
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Cultivation and Diagnosis

• Gram stain of specimen presumptive
  identification
• a-hemolytic
• optochin sensitivity
• Quellung test or capsular swelling reaction   The
  test consists of mixing a loopful of colony with
  equal quantity of specific antiserum and then
  examining microscopically at 1000X for capsular
  swelling.
• bile solubility

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Hemolysis patterns on blood agar
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Identification
Not optochin sensitive
Optochin sensitive
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• 4-The Viridans Streptococci
• Normal flora in the upper respiratory tract.
• alpha hemolysis or no hemolysis on Blood agar
• Do not possess Lancefield group antigens.
• Cases 50 and 70 of the bacterial endocarditis,
  especially in people with previously damaged
  heart valves. They are also frequently associated
  with bacteremia, deep wound infections, dental
  abscesses

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5-The Genus Enterococcus (Enterococcus faecalis)

• Enterococci are streptococci typically occurring
  in pairs and short chains
• Lancefield group D streptococci, these are
  non-hemolytic (gamma)
• Normal colonists of human large intestine
• Cause opportunistic urinary, wound, septicemia
  and endocarditis
• hydrolyze esculin and grow in the presence of 40
  bile salts

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• Laboratory diagnosis
• To distinguish group D streptococci, the Bile
  Esculin agar method is performed.
• Enterococci grow in the presence of the bile
  salts in the medium. They hydrolyze the esculin,
  producing esculetin which reacts with the iron
  salts in the medium turning the agar black