Chapter 15: Streptococci and Other

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• Chapter 15 Streptococci and Other
• Streptococci-like Organisms

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Streptococcus and Enterococcus General
Characteristics

• Gram-positive, facultatively anaerobic cocci
• They are aerotolerant, meaning that can grow in
  the presence of O2
• Most are typically spherical some may appear
  elongated
• They may appear in chains or pairs

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Streptococcus and Enterococcus General
Characteristics

• Catalase-and oxidase-negative

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Streptococcus and Enterococcus Habitat and
Clinical Infections

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

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

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Streptococcus and Enterococcus Cell Wall
Structure

• Thick peptidoglycan layer
• Teichoic acid
• Ccarbohydrate layer present except in viridans
  group
• C carbohydrates used in Lancefield grouping of
  Streptococcus spp. (EXCEPT S. pneumoniae and S.
  viridans)
• Groups A, B, C, D, etc.
• Capsule in S. pneumoniae and in young cultures of
  most species

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Streptococcus and Enterococcus

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

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Streptococcus and Enterococcus Hemolytic Patterns

• No hemolysis (gamma) colonies show no hemolysis
  or discoloration in isolated colonies (thick
  part of this plate looks alpha-hemolytic)

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Classification schemes

• Physiologic characteristics
• Pyogenic produce pus
• Lactococci found in dairy products
• Enterococci normal gut flora
• Viridans normal URT flora
• Serological grouping or typing of C carbohydrate
• Lancefield group
• Performed only on ß-hemolytic hemolysis
• Biochemical
• Based on hemolytic reaction of isolate

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Biochemical Identification

• Susceptibility tests
• Bacitracin (0.04 units) or A disk or Taxo A
  disk
• Identifies Group A streptococci (S. pyogenes)
• Zone of inhibition is presumptive ID of Grp. A
  strep

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 or Taxo P disk
• Differentiates S. pneumoniae from other
• alpha-hemolytic streptococci (Viridans group)

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Biochemical Identification

• Bile solubility test
• S pneumoniae lyses in a suspension of sodium
  deoxycholate while other viridans streptococci do
  not lyse (old test no longer in use, but seen
  frequently on certification exams)

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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
  forming a purple color

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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 (we use BE slants in lab instead of
  plates)
• 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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Biochemical Identification

• Streptococcus spp. can also be identified used
  latex agglutination kits. Latex beads are coated
  with group specific anti-serum, which clump when
  mixed with a small amount of colony from the
  specific Streptococcus sp.

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Clinically Significant Streptococci
Streptococcus pyogenes or Group A Beta-Hemolytic
Streptococci

• Bacterial Structure/Virulence Factors
• Fimbrae attachment and adherence ( protein F)
• M protein major virulence factor resistance to
  phagocytosis
• Hyaluronic acid capsule prevents phagocytosis
• Lipoteichoic acid adheres to molecules on host
  epithelial cells

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Streptococcus pyogenes or Group A Streptococci
Additional Virulence Factors

• Hemolysins
• Streptolysin O (O2 labile) detected in ASO titers
• Streptolysin S (O2 stable) Causes hemolysis on
  plates
• Erythrogenic toxin/Streptococcal pyogenic
  exotoxin scarlet fever
• Enzymes
• Streptokinase
• DNases
• Hyaluronidase spreading factor

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Streptococcus pyogenes (Group A) Streptococcal
Infections

• Acute bacterial pharyngitis/tonsillitis (about
  1/3 of all sore throats are strep throats)
• Sore throat
• Malaise
• Fever/headache
• Scarlet fever
• rash
• Pyodermal infections
• Impetigo weeping lesion
• Erysipelas
• Cellulitis

Erysipelas due to Streptococcus pyogenes
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Streptococcus pyogenes (Group A) Streptococcal
Infections
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Streptococcus pyogenes (Group A) Streptococcal
Infections

• Scarlet Fever (starts with pharyngitis and causes
  rash on trunk and extremities)

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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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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
  (most evidence favors cross-reactivity between
  Strep. antigens and heart tissue)
• ASO titer will be elevated

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PostGroup-A Streptococcal Infections

• Acute glomerulonephritis (AGN) 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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Laboratory Diagnosis Group A Streptococcus
Grams stained wound smear showing gram-positive
cocci in chains with numerous polys (PMNs)
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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
• SXT- resistant

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
  (10-30 rate can cause OB complications such as
  premature rupture of membranes and premature
  delivery)
• Cause invasive diseases in newborns
• Early-onset infection
• Late-onset disease

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Group B b-Hemolytic Streptococcus (Staphylococcus
agalactiae)

• Virulence Factors
• Capsule
• Hemolysin
• CAMP factor
• Neuraminidase
• Deoxyribonuclease
• Hyaluronidase
• Protease

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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 (Moms are screened 35-37 weeks gestation)
• 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
• Hippurate hydrolysis positive
• SXT- resistant

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
• S. bovis
• S. equinus
• 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
• Important to identify Enterococcus from
  non-Enterococcus, because Enterococcus must be
  treated more aggressively.

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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 (Viridans means green)
• Members of the normal oral, nasopharyngeal flora,
  GI tract and female genital tract
• 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)
• Also involved with gingivitis and dental carries

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Non- group D Streptococci Viridans

• 4 groups
• Anginosus
• S. anginosus, S. intermedius, S. constellatus
• Mitis
• S. sanguig, S. parasanguis, S. gordonii, S.
  crista, S. infantis, S. mitis, S. oralis, S.
  oralis, S. peroris
• Mutans
• S. criceti, S. downei, S. macacae, S. mutans, S.
  rattus, S. sobrinus
• Salivarius
• S. salivarius, S. thermophilus, S. vestibularis

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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 (most common cause of bacterial
  pneumonia)
• Meningitis
• Bacteremia
• Sinusitis/otitis media (most common cause of
  otitis media in children lt 3 years)
• Vaccine should be given to elderly and those
  without spleens

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Laboratory DiagnosisStreptococcus pneumoniae

• Microscopic morphology
• Gram-positive cocci in pairs lancet-shaped
  (somewhat oval in shape)

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Laboratory DiagnosisStreptococcus pneumoniae

• Colony morphology
• Smooth, glistening, wet-looking, mucoid
• a-Hemolytic
• CO2enhances growth
• As colony ages, autolytic collapse causes
  checker shape

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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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NVS Streptococcus

• Nutritionally variant streptococci
• Causes endocarditis and otitis media
• Can be normal throat flora
• Requires pyridoxal to grow (can satellite arouond
  Staph, E. coli, Klebsiella, Enterobacter and
  yeasts)

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Classification of Streptococcus and Enterococcus
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Streptococcus and Enterococcus

• Treatment
• Generally, streps are not routinely tested for
  susceptibility since penicillin drug of choice.
  If the patient is allergic to pen use
  erythromycin.
• Antibiotic resistance seen with Enterococcus, use
  vancomycin