E Streptococcus ST
E Streptococcus ST
E Streptococcus ST
Flesh-eating bacteria
Gram-Positive Cocci
Genus Streptococcus
I. General presentation
• Minidefinition:
– Gram positive cocci grouped in chains
involved in suppurative infections, toxinoses
(e.g.scarlet fever) and poststreptococcal
complications
Gram stain of Streptococcus
II. Taxonomy and classification
Bergey Manual 2004:
Domain: Bacteria
Phylum: B XIII, Firmicutes
Class: III, Bacilli
Order: Lactobacilalles
Family: Streptococcaceae
Genus Streptococcus
• Non-groupable streptococci:
- Str. pneumoniae
» Pneumonia, meningitis, recurrent otitis
- Str. mutans
- Str. viridans
» Dental caries
Classification based on hemolysis
• Beta
– Complete hemolysis
– Group A, C, G
• Alpha: partial hemolysis,
greenish colour:
– Str. pneumoniae, Str.
viridans
• Alpha’: partial hemolysis
– Group D (may be alpha’ or
gamma)
• Gamma
– Absence of hemolysis
Diseases caused by Streptococci
- Suppurative infections:
- Non invasive:
- Sore throat (Group A Streptococcus),
- Impetigo, erizipelus
- Invasive:
- New born meningitis (Group B Streptococcus),
- Necrotizing fasciitis (Group A streptococcus – flesh eating bacteria)
- Hospital acquired infections (Enterococcus);
- Pneumonia (Streptococcus pneumoniae) etc.
- Toxinoses: Scarlet fever, streptococcal toxic shock (pyrogenic toxin)
- Generalized infections: Bacteremia/septicemia/endocarditis (Enterococcus, Str.
pneumoniae, Str. viridans)
- Poststreptococcal complications - of medium or high severity
Pyrogenic toxin
• Superantigen
• Polyclonal Mitogen for T
lymphocytes
• Activates immunity system
causing delivery of pro-
inflammatory cytokines
Scarlet fever
CLINICAL FEATURES
-2-4 incubation period
- Headache and tonsillitis appear after
Rash:
- develops within 2 hours, spreads rapidly over trunk and neck
- With increased density in the neck, axillae and groins.
- A fine punctuate erythematous appearance
- A “sand papery” feel and blanching on pressure.
-Rash lasts about 6 days followed by peeling
Tongue:
- white first then “red strawberry”
Poststreptococcal complications
– early and late
• Acute Rheumatic Fever (ARF)
• Early – 2 to 4 weeks after the throat
infection: rheumatic arthritis (light): big
articulations, moving arthritis without
sequelae
• Rheumatic Heart Disease
• Usually after several episodes of ARF:
heart damage (severe) – damaged valves –
fibrillation, infection, heart failure,
thrombotic accidents
– Chronic sequelae, life threatening!!!
Rheumatic fever- mechanism
Streptococcal M Protein
– Cross-react with myosin
– Autoimmunity
Catalase negative;
Facultatively anaerobic bacteria
Resistence to physical, chemical
and biological agents
• Physical agents:
– Less resistant than Staphylococcus to:
• cold
• dryness
• pH variations
Major pathogenity factors
Cell wall antigens:
• Lipoteichoic acid/F protein
– Fimbria
– Attach to epithelium cells
• M Protein
– Anti-phagocytic
– Involved in natural and adaptive immunity (Ab)
– Several M types – reinfection is possible with a different
M type strain
• Capsule
– Anti-phagocytic
Str. pyogenes
lipoteichoic acid
F-protein
fibronectin
epithelial cells
Protein M
Complement IMMUNE
IgG
r
r r
M protein
peptidoglycan NON-IMMUNE
fibrinogen
r
r r
VII. Pathogenesis:
• Colonize skin and mucosal surfaces
(special superficial structures)
• Invazion and infectious process
• Toxins: erithrogenic, pyrogenic
• Structures to avoid immune response:
– Capsule
– Protein M
VIII. Immune response
• Main mechanism: fagocytosis
• Neutralising anti-toxic antibodies
• Antibody dependent Opsonisation
Bacteria resist by:
- Capsule and M protein, which interfere the
phagocytosis
Antigens cross-reacting with myosin are
responsible for autoimmunity (post-
streptococcal complications)
IX. Epidemiology and prophylaxis
- Humans are the reservoir for strep A
- Transmitted mainly by drops, less by direct contact
- Asymptomatic colonization in 20% of population
- Poststreptococcal complications: outbreak investigation;
Penicillin emergency treatment in severe streptococcal sore
throat and scarlet fever
- Enterococcus – zoonotic agent, nosocomial infections
- In toxic shock – fatality rate 30%
• Prophylaxis and treatment:
– Group A streptococcus severe infections – mandatory
Penicillin; hypersensitivity to Penicillin – test for
erythromycin and cephalosporines
Laboratory diagnostic
1. Sampling and transport:
– serogrouping: group A
Catalase
Bacterial culture + H2O2
www. biochemicaltestproject.blogspot.com
Hemolytic colonies
• Developed by Streptococcus group A
(SGA), G and C
• Identification of SGA
– Bacitracin test: inhibition of growth =
SGA
– Serological identification using group
specific sera
Bacitracin test for GAS
identification
Commercial agglutination test
+
Antibody
Liposome
Streptococcal antigen
GAS Serotyping
M types
Scope:
-Epidemiology:
T types
-To find the source and
R types
transmission pathway
Based on
-To differentiate a reinfection
cell wall
proteins -Case management:
structure -to evaluate the potential of
the strain to cause
poststreptococcal injury
Indirect diagnostic
Serological
• Antistreptolysin O (ASO)
• Important for monitoring
of strep A elimination and
poststreptococcal
disease
• Normal values: under 200
– 250 UI (for Romania)
Group B streptococcus
• Meningitis in new
borns
• Septicemia
• Transmission
– from vaginal flora of
the mother
– before or during birth
Group B Streptococcus
(Streptococcus agalactiae) identification
• Lysed by bile (#
str.viridans)
• Inuline positive (#
str.viridans)
Antimicrobial susceptibility
testing
• Usually not for SGA, because always
susceptible to Penicillin; test only for
Penicillin allergic patients, to Macrolides
and Cephalosporins
• Pneumococci usually susceptible to
Penicillin, Macrolides. For Penicillin
resistant strains test Cephalosporins and for
Cephalosporin resistant give Vancomycin
Key words Streptococcus:
• Gram positive, arranged in chains
• Sore throat, postinfectious complications, new born
meningitis, scarlet fever, pneumonia (Str.
pneumoniae)
• Catalase negative
• Lancefield groups, hemolysis; M types
• Group A – bacitracin test
• ASO test; Mandatory Penicillin in severe GAS
infections
• Group B – new born meningitis
• Viridans hemolysis + optochin positive = Str.
pneumoniae