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Streptococci and Other

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Title: Streptococci and Other


1
  • Streptococci and Other
  • Streptococci-like Organisms

2
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

3
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

4
Streptococcus and Enterococcus General
Characteristics
  • Gram-positive, facultatively anaerobic cocci
  • Most are typically spherical some may appear
    elongated

5
Streptococcus and Enterococcus General
Characteristics
  • Appear in chains when smears are prepared from
    broth cultures
  • Catalase-and oxidase-negative

6
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

7
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

8
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

9
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

10
Streptococcus and Enterococcus Hemolytic Patterns
  • No hemolysis (gamma) colonies show no hemolysis
    or discoloration

11
Classification of Streptococcus and Enterococcus
12
Biochemical Identification
  • Susceptibility tests
  • Bacitracin (0.04 units) or A disk
  • Identifies Group A streptococci

Group A streptococcus is susceptible to A disk
(left)
13
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
14
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

15
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
16
Biochemical Identification
  • Hydrolysis
  • Hippurate hydrolysis
  • Differentiates Group B streptococci from other
    beta hemolytic streptococci
  • Group B streptococci hydrolyzes sodium hippurate

17
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
18
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.
19
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

20
Streptococcus pyogenes or Group A Streptococci
Additional Virulence Factors
  • Hemolysins
  • Streptolysin O
  • Streptolysin S
  • Erythrogenic toxin
  • Enzymes
  • Streptokinase
  • DNases
  • Hyaluronidase

21
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
22
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

23
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

24
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

25
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

26
Laboratory Diagnosis Group A Streptococcus
Grams stained wound smear showing gram-positive
cocci in chains with numerous polys
27
Laboratory Diagnosis Group A Streptococcus
  • Colony morphology
  • Transparent, smooth, and well-defined zone of
    complete or b- hemolysis

28
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
29
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

30
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

31
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

32
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

33
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
34
Identification Schema
Schema to differentiate Group A and B from other
b-hemolytic streptococci
35
Streptococcus Group D and Enterococcus Species
  • Members of the gut flora
  • Associated infections
  • Bacteremia
  • Urinary tract infections
  • Wound infections
  • Endocarditis

36
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

37
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

38
Identification Schema
Schema to differentiate Enterococcus and Group D
streptococci from other nonhemolytic streptococci
39
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)

40
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

41
Laboratory DiagnosisStreptococcus pneumoniae
  • Microscopic morphology
  • Gram-positive cocci in pairs lancet-shaped

42
Laboratory DiagnosisStreptococcus pneumoniae
  • Colony morphology
  • Smooth, glistening, wet-looking, mucoid
  • a-Hemolytic
  • CO2enhances growth

43
Laboratory Diagnosis Streptococcus pneumoniae
  • Identification
  • Catalase negative
  • Optochin-susceptibility-testsusceptible
  • Bile-solubility-testpositive

44
Identification Schema
Schema to differentiate S. pneumoniae from other
a-hemolytic streptococci
45
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

46
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

47
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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