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Chapter 15: Streptococci and Other

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Title: Chapter 15: Streptococci and Other


1
  • Chapter 15 Streptococci and Other
  • Streptococci-like Organisms

2
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

3
Streptococcus and Enterococcus General
Characteristics
  • Catalase-and oxidase-negative

4
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

5
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

6
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

7
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

8
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)

9
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

10
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)
11
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
12
Biochemical Identification
  • Susceptibility test
  • Optochin P disk or Taxo P disk
  • Differentiates S. pneumoniae from other
  • alpha-hemolytic streptococci (Viridans group)

13
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)

14
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
15
Biochemical Identification
  • Hydrolysis
  • Hippurate hydrolysis
  • Differentiates Group B streptococci from other
    beta hemolytic streptococci
  • Group B streptococci hydrolyzes sodium hippurate
    forming a purple color

16
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
17
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.
18
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.

19
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

20
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

21
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
22
Streptococcus pyogenes (Group A) Streptococcal
Infections
23
Streptococcus pyogenes (Group A) Streptococcal
Infections
  • Scarlet Fever (starts with pharyngitis and causes
    rash on trunk and extremities)

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
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

27
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

28
Laboratory Diagnosis Group A Streptococcus
Grams stained wound smear showing gram-positive
cocci in chains with numerous polys (PMNs)
29
Laboratory Diagnosis Group A Streptococcus
  • Colony morphology
  • Transparent, smooth, and well-defined zone of
    complete or b- hemolysis

30
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
31
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

32
Group B b-Hemolytic Streptococcus (Staphylococcus
agalactiae)
  • Virulence Factors
  • Capsule
  • Hemolysin
  • CAMP factor
  • Neuraminidase
  • Deoxyribonuclease
  • Hyaluronidase
  • Protease

33
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

34
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

35
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

36
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
37
Identification Schema
Schema to differentiate Group A and B from other
b-hemolytic streptococci
38
Streptococcus Group D and Enterococcus Species
  • Members of the gut flora
  • S. bovis
  • S. equinus
  • Associated infections
  • Bacteremia
  • Urinary tract infections
  • Wound infections
  • Endocarditis

39
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

40
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.

41
Identification Schema
Schema to differentiate Enterococcus and Group D
streptococci from other nonhemolytic streptococci
42
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

43
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

44
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

45
Laboratory DiagnosisStreptococcus pneumoniae
  • Microscopic morphology
  • Gram-positive cocci in pairs lancet-shaped
    (somewhat oval in shape)

46
Laboratory DiagnosisStreptococcus pneumoniae
  • Colony morphology
  • Smooth, glistening, wet-looking, mucoid
  • a-Hemolytic
  • CO2enhances growth
  • As colony ages, autolytic collapse causes
    checker shape

47
Laboratory Diagnosis Streptococcus pneumoniae
  • Identification
  • Catalase negative
  • Optochin-susceptibility-testsusceptible
  • Bile-solubility-testpositive

48
Identification Schema
Schema to differentiate S. pneumoniae from other
a-hemolytic streptococci
49
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)

50
Classification of Streptococcus and Enterococcus
51
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
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