Streptococci and Other
Streptococci-like Organisms
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
 Clinical infections
 Indigenous respiratory
tract microbial flora of
animals and humans
 Certain species are also
found in the
gastrointestinal and
urogenital tracts of
humans
 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
 C=carbohydrate 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
Species
S.pyogenes
ß
Group
Antigen
A
S.agalactiae
ß
B
Group B
streptococci
S. equisimilis
ß
C
E. faecalis
E. faecium
E. durans
Alpha or no
hemolysis
( rarely ß )
D
Group C
streptococci
Enterococci
S. bovis
S. equinus
Alpha ()or
none
(rarely ß)
D
Nonenterococci
S. pneumoniae
Viridans and
Nonhemolytic
S. sanguis
S. salivarius
S. mitis or
nonhemolytic
S. milleri
S. mutans
Hemolysis
Alpha ()
hemolysis
Alpha ()
hemolysis or
no
hemolysis
-
Common
Terms
Group A
streptococci
Disease Association(s)
Pharyngitis; scarlet fever
pyoderma; rheumatic
fever; AGN
Neonatal sepsis;
puerperal fever;
pyogenic infections;
pneumonia; meningitis
Pharyngitis; impetigo;
pyogenic infections
Urinary tract infections
Wound infections
Bacteremia;
Endocarditis
Urinary tract; pyogenic
infections;
Endocarditis infections
Pneumococcus
Bacteremia;
pneumonia;
meningitis;
Viridans strep
Endocarditis
Dental caries
Other species
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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-pyrrolidonylb-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, MunchPetersen (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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Post–Group-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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Post–Group-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-esculin–negative
 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 bhemolysis
 Presumptive Identification
tests
 Catalase-negative
 Bacitracin-resistant
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Laboratory Diagnosis:
Group B b-Hemolytic Streptococcus
 Presumptive identification
tests
 Bile-esculin-hydrolysis–
negative
 Does not grow in 6.5%
NaCl
 CAMP-test–positive
S. agalactiae shows the arrowshaped 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
- 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 Diagnosis:
Streptococcus pneumoniae
 Microscopic morphology
 Gram-positive cocci in
pairs; lancet-shaped
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Laboratory Diagnosis:
Streptococcus pneumoniae
 Colony morphology
 Smooth, glistening,
wet-looking,
mucoid
 -Hemolytic
 CO2enhances
growth
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Laboratory Diagnosis:
Streptococcus pneumoniae
 Identification
 Catalase negative
 Optochinsusceptibility-test–
susceptible
 Bile-solubility-test–
positive
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Identification Schema
Schema to differentiate S.
pneumoniae from other hemolytic streptococci
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Streptococcus-Like Organisms
 Aerococcus
 Gram-positive cocci that tend to form tetrads
 -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
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