Streptococci and Other

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• Streptococci and Other
• Streptococci-like Organisms

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Case Study

• 9-year-old boy complains of fever and sore throat
• On examination, his pharynx is red and his
  tonsils are swollen
• His cervical lymph nodes are also swollen
• A throat culture is taken

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Points to Consider

• Clinical symptoms presented by the patient
• The serious complications that may result from
  this type of infection
• How to recover and identify the infecting
  organism
• What other species are involved in clinical
  infections
• Other points to consider

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Streptococcus and Enterococcus General
Characteristics

• Gram-positive, facultatively anaerobic cocci
• Most are typically spherical some may appear
  elongated

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Streptococcus and Enterococcus General
Characteristics

• Appear in chains when smears are prepared from
  broth cultures
• Catalase-and oxidase-negative

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Streptococcus and Enterococcus Habitat and
Clinical Infections

• Habitat
• Indigenous respiratory tract microbial flora of
  animals and humans
• Certain species are also found in the
  gastrointestinal and urogenital tracts of humans

• Clinical infections
• Upper and lower respiratory tract infections
• Urinary tract infections
• Wound infections
• Endocarditis

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Streptococcus and Enterococcus Cell Wall
Structure

• Thick peptidoglycan layer
• Teichoic acid
• Ccarbohydrate layer present except in viridans
  group
• Capsule in S. pneumoniae and in young cultures of
  most species

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Streptococcus and Enterococcus General
Characteristics

• Hemolytic Patterns
• Beta (ß) a clear, colorless zone around the
  colony caused by complete hemolysis of the red
  blood cells in the agar

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Streptococcus and Enterococcus Hemolytic Patterns

• Alpha (a)hemolysis showing a greenish
  discoloration around the area surrounding the
  colony due to incomplete hemolysis of the red
  blood cells in the agar

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Streptococcus and Enterococcus Hemolytic Patterns

• No hemolysis (gamma) colonies show no hemolysis
  or discoloration

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Classification of Streptococcus and Enterococcus
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Biochemical Identification

• Susceptibility tests
• Bacitracin (0.04 units) or A disk
• Identifies Group A streptococci

Group A streptococcus is susceptible to A disk
(left)
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Biochemical Identification

• Susceptibility test
• Trimethoprim sulfamethoxazole (SXT)
• Inhibits beta-hemolytic streptococcal groups
  other than A and B

Group A streptococcus growing in the presence of
SXT
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Biochemical Identification

• Susceptibility test
• Optochin P disk
• Differentiates S. pneumoniae from other
  alpha-hemolytic streptococci (Viridans group)
• Bile solubility test
• S pneumoniae lyses in a suspension of sodium
  deoxycholate while other viridans streptococci do
  not lyse

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Biochemical Identification

• PYR hydrolysis
• Substrate L-pyrrolidonyl-b-napthlyamide (PYR) is
  hydrolyzed by Group A Streptococci and
  Enterococcus sp.
• As specific as 6.5 NaCl broth for Enterococcus
  sp.
• More specific than Bacitracin for Group A
  streptococci

PYR test for Group A streptococci and
enterococci. Both are positive for this test
(right) left is a negative result
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Biochemical Identification

• Hydrolysis
• Hippurate hydrolysis
• Differentiates Group B streptococci from other
  beta hemolytic streptococci
• Group B streptococci hydrolyzes sodium hippurate

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Biochemical Identification

• Christie-Atkins, Munch-Petersen (CAMP) test
• Detects the production of enhanced hemolysis that
  occurs when b-lysin and the hemolysins of Group B
  streptococci come in contact

Group B streptococci showing the classical
arrow-shaped hemolysis near the staphylococcus
streak
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Biochemical Identification

• Bile Esculin hydrolysis
• Ability to grow in 40 bile and hydrolyze Esculin
  are features of streptococci that possess Group
  D antigen
• Growth in 6.5 NaCl broth
• Differentiates Group D streptococci from
  enterococci

Both Group D streptococci and enterococci produce
a positive (left) bile Esculin hydrolysis test.
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Clinically Significant Streptococci
Streptococcus pyogenes or Group A Beta-Hemolytic
Streptococci

• Bacterial structure
• Fimbrae attachment and adherence
• M protein major virulence factor
• Hyaluronic acid capsule prevents phagocytosis

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Streptococcus pyogenes or Group A Streptococci
Additional Virulence Factors

• Hemolysins
• Streptolysin O
• Streptolysin S
• Erythrogenic toxin
• Enzymes
• Streptokinase
• DNases
• Hyaluronidase

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Streptococcus pyogenes (Group A) Streptococcal
Infections

• Acute bacterial pharyngitis
• Sore throat
• Malaise
• Fever/headache
• Scarlet fever
• Pyodermal infections
• Impetigo
• Erysipelas

Erysipelas due to Streptococcus pyogenes
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PostGroup-A Streptococcal Infections

• Rheumatic fever from pharyngeal infections only
• Fever
• Inflammation of the heart, joints, blood vessels,
  and subcutaneous tissues
• Chronic, progressive damage to the heart valves

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PostGroup-A Streptococcal Infections

• Acute glomerulonephritis from either cutaneous or
  pharyngeal infections
• More common in children than adults
• Antigen-antibody complexes deposit in the
  glomerulus
• Inflammatory response causes damage to the
  glomerulus and impairs the kidneys

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Invasive Group A Streptococcal Infections

• Streptococcal toxic shock syndrome
• Multi-organ system failure similar to
  staphylococcal toxic shock
• Initial infection may have been pharyngitis,
  cellulitis, peritonitis, or other wound infections

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Invasive Group A Streptococcal Infections
Flesh-Eating Bacteria

• Cellulitis
• Severe form of infection that is life-threatening
• Bacteremia and sepsis may occur
• In patients necrotizing fasciitis, edema,
  erythema, and pain in the affected area may
  develop
• Streptococcal myositis resembles clostridial
  gangrene

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Laboratory Diagnosis Group A Streptococcus
Grams stained wound smear showing gram-positive
cocci in chains with numerous polys
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Laboratory Diagnosis Group A Streptococcus

• Colony morphology
• Transparent, smooth, and well-defined zone of
  complete or b- hemolysis

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Laboratory Diagnosis Group A Streptococcus

• Identification
• Catalase-negative
• Bacitracin-susceptible
• PYR-positive
• Bile-esculinnegative
• 6.5 NaCl-negative

Group A streptococci is susceptible to Bacitracin
disk (left) The right shows resistance
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Group B b-Hemolytic Streptococcus (Staphylococcus
agalactiae)

• Has been known to cause mastitis in cattle
• Colonize the urogenital tract of pregnant women
• Cause invasive diseases in newborns
• Early-onset infection
• Late-onset disease

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Staphylococcus agalactiae Invasive Infections

• Early-onset infection
• Occurs in neonates who are less than 7 days old
  neonates
• Vertical transmission of the organism from the
  mother
• Manifests in the form of pneumonia or meningitis
  with bacteremia
• Associated with a high mortality rate

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Staphylococcus agalactiae Invasive Infections

• Late-onset infection
• Occurs between 1 week and 3 months after birth
• Usually occurs in the meningitis form
• Mortality rate is not as high as early-onset
• In adults
• Occurs in immunosuppressed patients or those with
  underlying diseases
• Often found in a previously healthy adult who
  just experienced childbirth

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Laboratory Diagnosis Group B b-Hemolytic
Streptococcus

• Colony morphology
• Grayish-white, mucoid, creamy, narrow zone of
  b-hemolysis
• Presumptive Identification tests
• Catalase-negative
• Bacitracin-resistant

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Laboratory Diagnosis Group B b-Hemolytic
Streptococcus

• Presumptive identification tests
• Bile-esculin-hydrolysisnegative
• Does not grow in 6.5 NaCl
• CAMP-testpositive

S. agalactiae shows the arrow-shaped hemolysis
near the staphylococcus streak, showing a
positive test for CAMP factor
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Identification Schema
Schema to differentiate Group A and B from other
b-hemolytic streptococci
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Streptococcus Group D and Enterococcus Species

• Members of the gut flora
• Associated infections
• Bacteremia
• Urinary tract infections
• Wound infections
• Endocarditis

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Laboratory Diagnosis Streptococcus Group D and
Enterococcus Species

• Microscopic morphology
• Cells tend to elongate
• Colony morphology
• Most are non-hemolytic, although some may show a-
  or, rarely, b-hemolysis
• Possess Group D antigen

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Laboratory Diagnosis Streptococcus Group D and
Enterococcus Species

• Identification tests
• Catalase may produce a weak catalase reaction
• Hydrolyze bile esculin
• Differentiate Group D from Enterococcus sp. with
  6.5 NaCl or PYR test

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Identification Schema
Schema to differentiate Enterococcus and Group D
streptococci from other nonhemolytic streptococci
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Other Streptococcal Species

• Viridans group
• Members of the normal oral and nasopharyngeal
  flora
• Includes those that lack the Lancefield group
  antigen
• Most are ? hemolytic but also includes
  nonhemolytic species
• The most common cause of subacute bacterial
  endocarditis (SBE)

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Streptococcus pneumoniae

• General characteristics
• Inhabits the nasopharyngeal areas of healthy
  individuals
• Typical opportunist
• Possess C substance
• Virulence factors
• Polysaccharide capsule
• Clinical infections
• pneumonia
• meningitis
• bacteremia
• sinusitis/otitis media

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Laboratory DiagnosisStreptococcus pneumoniae

• Microscopic morphology
• Gram-positive cocci in pairs lancet-shaped

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Laboratory DiagnosisStreptococcus pneumoniae

• Colony morphology
• Smooth, glistening, wet-looking, mucoid
• a-Hemolytic
• CO2enhances growth

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Laboratory Diagnosis Streptococcus pneumoniae

• Identification
• Catalase negative
• Optochin-susceptibility-testsusceptible
• Bile-solubility-testpositive

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Identification Schema
Schema to differentiate S. pneumoniae from other
a-hemolytic streptococci
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Streptococcus-Like Organisms

• Aerococcus
• Gram-positive cocci that tend to form tetrads
• a-hemolytic and may resemble viridans group
• May be confused with Enterococcus biochemically

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Streptococcus-Like Organisms

• Leuconostoc
• Resemble streptococci microscopically colonies
  resemble viridans group or Enterococcus
• Found in plants, vegetables, and dairy products
• Pediococcus
• Found in nature used in bioprocessing and
  biopreservation of foods such as cheese, meats,
  and vegetables
• Rarely seen in human infections has been
  associated with septicemia

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Points to Remember

• General characteristics and hemolytic patterns
  of
• streptococcal and enterococcal species
• Infections produced by pathogenic species
• Microscopic and colony morphology
• Tests used to identify these species
• Emergence of resistant strains