Streptococcus Flashcards
Family Streptococcaceae
• Divided into 3 genera: (Bergey’s Manual of Determinative Bacteriology
)
• Streptococcus
• Enterococcus
• Lactococcus
Streptococci: General Characteristics
• Gram Positive Cocci in pairs or chains
• CATALASE____
• Fastidious → media??
• Colonies:_____
• With____ hemolytic zones
• Facultative anaerobes & needs_____ for growth
• Non-motile & Non-spore forming
Negative
BAP, CAP, Todd-Hewitt broth
Small, pinpoint, and translucent
large
5-10% CO2
Streptococci: Classification
• Patterns of Hemolysis
• Physiologic Requirement
• Lancefield Antigen Grouping
: Antigenic character in the polysaccharide cell wall
• Lancefield Antigen Grouping
: Antigenic character in the polysaccharide cell wall
• Lancefield Antigen Grouping
(Smith & Brown Classification)
J.H. Brown, 1919
Patterns of Hemolysis
Alpha hemolytic
• Incomplete or partial hemolysis of RBC
• green discoloration
S. pneumoniae
S viridans
Beta hemolytic
• complete hemolysis of RBC
• clear or colorless zone of hemolysis surrounding bacterial colony
S pyogenes
S agalactiae
Gamma hemolytic
Non-hemolytic
Enterococcus
(Bergey’s/Academic Classification)
Sherman 1937
Physiological Division
→ includes beta hemolytic strains ABCEFG
Pyogenic division
> not beta hemolytic, not salt tolerant, and grow at high pH
Viridans division
> salt tolerant, grow at high pH, and Temp range of 10°C to 45°C
Enterococcus division
> not clinically significant & associated with dairy industry
Lactic division
• Divides the Streptococci into serologic groups
• A, B, C, D, E (first 5)
Rebecca Lancefield (1933)
Rebecca Lancefield (1933)
• Currently: almost____ groups = (A - H) & (K - T)
•____ Testing
• Clinically Significant:___
20
Serological
A, D, C, D, F, G
Beta Hemolytic Streptococcus
Lancefield group A
Lancefield group B
Lancefield group C & G
Lancefield group A, C, F & G
• S. pyogenes
• S. agalactiae
• S. dysgalactiae & S. equi
• S. anginosus
• Not a normal flora
• Most virulent for humans
Group A: Streptococcus pyogenes (GAS)
Disease:
• Bacterial pharyngitis
• Skin infections
• Invasive diseases
Group A: Streptococcus pyogenes (GAS)
• Complications:
• Rheumatic Heart Disease
• Acute Glomerulonephritis
Group A: Streptococcus pyogenes (GAS)
Group A: Streptococcus pyogenes (GAS)
• Transmission:
• Person to person contact
• Aerosol droplets
Group A: Streptococcus pyogenes (GAS)
Major Virulence Factors
CELL SURFACE ANTIGENS
- Hyaluronic acid Capsule
- M protein
- Group-specific cell wall antigen
- IgG & IgA-binding proteins
- C5a protease
- F protein
- Lipoteichoic acid
• 80 types
• inhibits activation of complement
• Anti-phagocytic
M protein
Group-specific cell wall antigen:
• Grp.A sugar:
Rhamnose-N-acetylglucosamine
• Binds to Fc region of IgG or lgA.
IgG & IgA-binding proteins
• cleaves C5a component of complement
• inhibits neutrophil chemotaxis in vitro
C5a protease
- allows binding to fibronectin in pharyngeal epithelium
F protein
• attached to M protein.
• may allow binding to fibronectin
Lipoteichoic acid
Group A: Streptococcus pyogenes (GAS)
Major Virulence Factors
ENZYMES & TOXINS
- Streptokinase
- Streptodornase
- Hyaluronidase
- Diphosphopyridine Nucleotidase
- Pyrogenic Exotoxins / Erythrogenic Toxins A, B, C
- Streptolysin O
- Streptolysin S
: Fibrinolysin that lyses blood clots
Streptokinase
: degrades host DNA & RNA
Streptodornase
• Associated with the organism’s ability to destroy WBCs
Diphosphopyridine Nucleotidase
• Associated with fever and rashes in scarlet fever
• Streptococcal TSS
Pyrogenic Exotoxins / Erythrogenic Toxins A, B, C
• Antigenic (Anti-Streptolysin O)
• Also produced by Group C & G
• Oxygen labile
Streptolysin O
• Oxygen stable
• surface hemolysin
• Antiphagocytic
• Toxic to various human cell types
Streptolysin S
Pathogenesis and Clinical
Manifestations
PYOGENIC DISEASES
• Erysipelas
• Cellulitis
• Impetigo
• Streptococcal Pharyngitis
GAS pyogenes
TOXIGENIC DISEASES
• Necrotizing fasciitis
•Scarlet Fever
•Streptococcal Toxic Shock Syndrome
GAS pyogenes
S. pyogenes grows in infected wound
»> Bacteria enter bloodstream & secrete exotoxin A»_space;>
Fever, rash, shock, bacteremia, respiratory failure (50% death rate)
Post-streptococcal Diseases
• Preceeded by skin or respiratory infections
• Represents a hypersensitivity response
• Immune-mediated
Rheumatic heart disease
Acute rheumatic fever
Acute glomerulonephritis
Diagnostic Laboratory Tests
A. MICROSCOPIC:
B. CULTURE:
• gram (+) cocci in pairs or chains
• 18-24 hrs.
• @ 37C with 5-10% CO2
GAS
CULTURE:
•
BAP: white to gray pinpoint colonies, translucent, opalescent.
18-24 hrs. @ 37C with 5-10% CO2
GAS
BAP: white to gray pinpoint colonies, translucent, opalescent.
• Wide zone of B-hemolysis
• Contaminated (throat): BAP with SXT
• Mucoid colonies: M-CHON (+)
GAS
Diagnostic Laboratory Tests
C. BIOCHEMICAL :
- Catalase
- BAP WITH SXT =
- Taxo A/Bacitracin Disk test
0.02 to 0.04 unit
Any zone of inhibition - PYR Test:
PYR Test: Pyrrolidonyl arylamidase test
• Reagent:
L-pyrrolidonyl-2-naphthylamide
PYR test
P-naphthylamide + p-dimethylaminocinnamaldehyde
(PYRase)
→
Pink color
GAS
SEROLOGICAL TEST:
• ASO (anti-streptolysin 0)
• Sero typing of specific M CHON
SCARLET FEVER SUSCEPTIBILITY TESTS
- DICK TEST
- SCHULTZ-CHARLTON TEST
• 0.1ml toxin (test arm) & 0.1ml toxoid (control arm)
• Observe for 24 hrs.
• (+) redness in test arm (1 cm)
• Susceptible to scarlet fever
DICK TEST
: (blanching phenomenon)
• Inject 0.1 mL of anti-toxin subcutaneously
• (+) fadind o redness after 6 to 8 hours
• Neutralization of erythrogenic toxin
SCHULTZ-CHARLTON TEST
