Title: Chapter 15: Streptococci and Other
1- Chapter 15 Streptococci and Other
- Streptococci-like Organisms
2Streptococcus 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
3Streptococcus and Enterococcus General
Characteristics
- Catalase-and oxidase-negative
4Streptococcus 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
5Streptococcus 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
6Streptococcus 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
-
7Streptococcus 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
8Streptococcus and Enterococcus Hemolytic Patterns
- No hemolysis (gamma) colonies show no hemolysis
or discoloration in isolated colonies (thick
part of this plate looks alpha-hemolytic)
9Classification 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
10Biochemical 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)
11Biochemical 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
12Biochemical Identification
- Susceptibility test
- Optochin P disk or Taxo P disk
- Differentiates S. pneumoniae from other
- alpha-hemolytic streptococci (Viridans group)
13Biochemical 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)
14Biochemical 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
15Biochemical Identification
- Hydrolysis
- Hippurate hydrolysis
- Differentiates Group B streptococci from other
beta hemolytic streptococci - Group B streptococci hydrolyzes sodium hippurate
forming a purple color
16Biochemical 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
17Biochemical 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.
18Biochemical 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.
19Clinically 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
20Streptococcus 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
21Streptococcus 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
22Streptococcus pyogenes (Group A) Streptococcal
Infections
23Streptococcus pyogenes (Group A) Streptococcal
Infections
- Scarlet Fever (starts with pharyngitis and causes
rash on trunk and extremities)
24Invasive 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
25Invasive 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
26PostGroup-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
27PostGroup-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
28Laboratory Diagnosis Group A Streptococcus
Grams stained wound smear showing gram-positive
cocci in chains with numerous polys (PMNs)
29Laboratory Diagnosis Group A Streptococcus
- Colony morphology
- Transparent, smooth, and well-defined zone of
complete or b- hemolysis
30Laboratory 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
31Group 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
32Group B b-Hemolytic Streptococcus (Staphylococcus
agalactiae)
- Virulence Factors
- Capsule
- Hemolysin
- CAMP factor
- Neuraminidase
- Deoxyribonuclease
- Hyaluronidase
- Protease
33Staphylococcus 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
34Staphylococcus 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
35Laboratory Diagnosis Group B b-Hemolytic
Streptococcus
- Colony morphology
- Grayish-white, mucoid, creamy, narrow zone of
b-hemolysis - Presumptive Identification tests
- Catalase-negative
- Bacitracin-resistant
36Laboratory 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
37Identification Schema
Schema to differentiate Group A and B from other
b-hemolytic streptococci
38Streptococcus Group D and Enterococcus Species
- Members of the gut flora
- S. bovis
- S. equinus
- Associated infections
- Bacteremia
- Urinary tract infections
- Wound infections
- Endocarditis
39Laboratory 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
40Laboratory 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.
41Identification Schema
Schema to differentiate Enterococcus and Group D
streptococci from other nonhemolytic streptococci
42Other 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
43Non- 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
44Streptococcus 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
45Laboratory DiagnosisStreptococcus pneumoniae
- Microscopic morphology
- Gram-positive cocci in pairs lancet-shaped
(somewhat oval in shape)
46Laboratory DiagnosisStreptococcus pneumoniae
- Colony morphology
- Smooth, glistening, wet-looking, mucoid
- a-Hemolytic
- CO2enhances growth
- As colony ages, autolytic collapse causes
checker shape
47Laboratory Diagnosis Streptococcus pneumoniae
- Identification
- Catalase negative
- Optochin-susceptibility-testsusceptible
- Bile-solubility-testpositive
48Identification Schema
Schema to differentiate S. pneumoniae from other
a-hemolytic streptococci
49NVS 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)
50Classification of Streptococcus and Enterococcus
51Streptococcus 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