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Streptococci (Gram
positive cocci)
Lecture 37
Faculty: Dr. Alvin Fox
1
Key Words
• Lancefield groups
• Hemolysis (alpha, beta, gamma)
• Group A streptococcus (S. pyogenes)
- Bacitracin susceptibility test
- M, T, R proteins
- Streptolysins O and S
- F protein/lipoteichoic acid
- Rheumatic fever/carditis/arthritis
- Glomerulonephritis
- Scarlet fever
- Toxic shock-like syndrome
- Bacteremia
- Flesh-eating bacteria
- Pyrogenic toxin
- Erythrogenic toxin
• Group B streptococcus (S.agalactiae)
- Neonatal septicemia/meningitis
- CAMP test
- Hippurate hydrolysis test
• Group D streptococcus
- Urinary tract infection
- Endocarditis
- Bile-esculin test
- Enterococci
- Non-enterococci
• Large colony
• Minute colony
• Viridans streptococci
• Dental caries/endocarditis
2
• Streptococci
– facultative anaerobe
– Gram-positive
– usually chains (sometimes pairs)
– catalase negative
(staphylococci are catalase positive)
3
Streptococcus in chains (Gram stain)
4
Streptococcus pneumoniae (diplococcus). Fluorescent stain
5
Identification : Lancefield groups
- carbohydrate antigens
6
groupable streptococci
• A, B and D
– frequent
• C, G, F
– less frequent
7
Non-groupable
• S. pneumoniae
– pneumonia
• viridans streptococci
– e.g. S. mutans
*dental caries
8
hemolysis reaction - sheep blood agar
• α (alpha)
– partial hemolysis
– green color
• β (beta)
– complete clearing
White colonies
• γ (gamma)
- no lysis
9
Hemolysis
• Groups A an B
–β
• Group D
– α or γ
• S. pneumoniae and viridans
–α
10
Identification:
hemolysis reaction
+ one biochemical characteristic
11
Group A streptococcus (S. pyogenes)
12
Group A streptococcal infections affect all ages
peak incidence at 5-15 years of age
13
S. pyogenes -suppurative
• non-invasive
– pharyngitis
– skin infection, impetigo
• invasive bacteremia
– toxic shock-like syndrome
– "flesh eating" bacteria
– pyrogenic toxin
14
Pyrogenic toxin
• Superantigen
• Non-specific activation of T cells
− Cross-link antigen presenting
cells (MHC) and T cell receptor
− Cytokine production
15
Scarlet fever
• rash
• “erythrogenic toxin”
16
non-suppurative
• rheumatic fever
– inflammatory disease
– life threatening
– chronic sequalae
• fever
• heart
• joints
• rheumatic NOT rheumatoid arthritis
17
Rheumatic fever -etiology
• M protein
– cross-reacts heart myosin
– autoimmunity
• Cell wall antigens
– poorly digested in vivo
– persist indefinitely
18
Rheumatic fever
• penicillin
- terminates pharyngitis
- decreases carditis
19
Acute glomerulonephritis
• immune complex disease of kidney
20
Major pathogenesis factors
• lipoteichoic acid/F protein
– fimbriae
– binds to epithelial cells
• M protein
– anti-phagocytic
21
S. pyogenes
lipoteichoic acid
F-protein
fibronectin
epithelial cells
22
M protein
IMMUNE
Complement
IgG
r
r
r
M protein
NON-IMMUNE
peptidoglycan
fibrinogen
r
r
r
23
M protein
• major target
– natural immunity
• strain variation
– antigenicity
• re-infection
– occurs with different strain
24
Capsules
• Anti-phagocytic
– mucoid strains
25
Isolation and identification
• β hemolytic colonies
– bacitracin inhibits growth
• β hemolytic colonies
– group A antigen
26
β hemolysis
• Hemolysin/streptolysin O
– sensitive oxygen
• Hemolysin/streplysin S
– insensitive oxygen
27
Modern Rapid “Strep” Test
Throat swab extract
(+/- streptococcal antigen)
-
+
Antibody
Liposome
Streptococcal antigen
28
Post-infectious diagnosis
(serology)
• antibodies to streptolysin O
• important if delayed clinical
sequelae occur
29
Typing
Traditional serotyping of
proteins:
-M
-T
-R
Current:
- Sequencing of M protein gene
30
Group B streptococcus
• neonatal meningitis
• septicemia
• transmission
– vaginal flora
31
Group B streptococcus
- identification
• β hemolysis
• hippurate hydrolysis
• CAMP reaction
– increases β hemolysis of S. aureus
32
Group D streptococcus
• Growth on bile esculin agar
– black precipitate
• 6.5% saline
• grow
– enterococci
• no growth
– non-enterococci
33
Enterococci
• distantly related to other streptococci
• genus Enterococcus
• gut flora
– urinary tract infection
• fecal contamination
– opportunistic infections
• particularly endocarditis
• most common E. (S.) faecalis
34
Enterococci
• resistant to many antibiotics
– including vancomycin
• terminal D-ala replaced by D-lactate
35
Minute colony streptococci
Various groups/hemolysis (e.g. group A)
– genetically distinct
from large colony (e.g. S. pyogenes)
– no rheumatic fever
Large colony
Minute colony
36
Viridans streptococci
•
•
•
•
•
•
diverse species
oral
dental caries
α hemolytic and negative for other tests
non-groupable.
includes S. mutans
– occassional endocarditis after tooth extraction
37