Download Streptococcus

Streptococcus(gram positive
coccus)
Dr. Hala Al Daghistani
Streptococci
Facultative anaerobe
Gram-positive
usually chains (sometimes pairs)
Catalase negative
Non motile
Hemolysins
Lancefield Groups (C-carbohydrate
in cell wall)
18 antigens
2
The streptococci are gram-positive spherical bacteria that
characteristically form pairs or chains during growth. some are
members of the normal human microbiota; others are associated
with important human diseases. No one system suffices to classify
them.
CLASSIFICATION
A. HEMOLYSIS
Many streptococci are able to hemolysed RBCs in vitro in varying
degrees.
Complete disruption of erythrocytes with clearing of the blood
around the bacterial growth is called β - hemolysis.
Incomplete lysis of erythrocytes with reduction of hemoglobin and
the formation of green pigment is called α - hemolysis.
Other streptococci are nonhemolytic (sometimes called γhemolysis).
b. Group-Specific Substance (Lancefield Classification)
This carbohydrate is contained in the cell wall of many
Streptococci and forms the basis of serologic grouping into
lancefield groups: a – h and k – u.
c. Capsular Polysaccharides
The antigenic specificity of the capsular polysaccharides is
used to classify Streptococcus pneumoniae into more than 90
types .
Strep Virulence Factors
 M- PROTEIN
- major target (hair like projection)
- strain variation (antigenicity)
- re-infection occurs with different strain
(150, types of M protein, a person can have
repeated infections with S pyogenes of
different M types).
• lipoteichoic acid ( attachment of
streptococci to epithelial cells).
Capsule ( Anti-phagocytic) (mucoid strains)
7
8
Virulence factors of S. pyogenes
• Streptolysin( O & S), Antistreptolysin O (ASO) . ASO
serum titer in excess of 160–200 units is considered
abnormally . (S = O2 stable; O = O2 labile)
– Streptokinase (Break down clots)
– DNase (depolymerize)
– Hyaluronidase
– Proteases
– C5a peptidase (Decrease chemotaxis)
• Toxins (Exotoxins)
– Pyrogenic toxin (Erythrogenic toxin A, B, C),
responsible for Streptococcal Toxic Shock Syndrome
and Scarlet Fever (superantigens)
Increase immune cytokines
 Promote fever
Streptococcal infections
Streptococcus pyogenes
A. Diseases attributable to invasion by S. pyogenes( β-hemolytic group
A- Streptococci)
Puerperal Fever, Cellulitis, Erysipelas, Bacteremia or sepsis, Necrotizing
fasciitis (Streptococcal Gangrene, flesh eating bacteria).
B. Diseases attributable to local infection with S. pyogenes and their
byproducts
Streptococcal Sore throat, Streptococcal infection of superficial layers
of skin( Impetigo),
C. Invasive Toxigenic group a Streptococcal infections, Streptococcal
toxic shock syndrome, and Scarlet fever
D. Poststreptococcal diseases (Rheumatic fever, GlomerulonephritisSpeB)
Streptococcus pyogenes
Streptococcus agalactiae
Group B Streptococci are part of the normal vaginal
flora and lower gastrointestinal tract in 5–30% of
women.
Infection during the first month of life may present as
Fulminant sepsis, Meningitis, or Respiratory distress
syndrome.
Important pathogens among pregnant women and
their neonates.
Viridans Streptococcus
The Viridans Streptococci are the most prevalent
members of the normal microbiota of the URT.
- principal cause of endocarditis on normal and
abnormal heart valves.
Viridans Streptococcus
• Alpha hemolysis
• No Lancefield groups
• Diseases
– Dental Caries
– Endocarditis
– Examples
• Strep mitis
• Strep mutans
• Strep oralis
• Strep sanguis
• Strep salivarius
Streptococcus pneumonia
The Pneumococci (S. pneumoniae) are gram-positive
diplococci
- lancet shaped or arranged in chains
- possessing a capsule of polysaccharide (91 type)
- pneumococci are normal inhabitants of the URT of 5–40%
of humans and can cause pneumonia, sinusitis, otitis,
bronchitis, bacteremia, meningitis, and other infections.
Strep. pneumoniae
Quellung Reaction
When pneumococci of a certain type are mixed with specific
antipolysaccharide serum of the same type—or with polyvalent
antiserum (OMNISERUM)—on a microscope slide