Streptococci and Other Streptococci-like Organisms
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Transcript Streptococci and Other Streptococci-like Organisms
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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