Streptococcus Flashcards
Characteristics of Streptococci
Gram-positive cocci arranged in pairs or chains
Most species are facultatively anaerobic
Ferment carbohydrates resulting in lactic acid production
Catalase negative (as opposed to staphylococci)
Classification of Streptococci
1) Cell wall carbohydrate antigens recognized by specific antibodies
2) Hemolytic pattern on agar containing blood cells
3) Biochemical properties
Hemolytic Pattern on agar containing blood cells
Alpha - partial hemolysis or “greening”
Beta - Complete clearing
Gamma - no change in red blood cells
Lancefield typing can recognize…
Group A Streptococci = S. pyogenes
Group B Streptococci = S. agalactiae
Group C = S. Dysgalactiae
Group F = S. Anginosus
S. Pyogenes pathology
Pharyngitis
Skin and soft tissue infections
Rheumatic fever
Glomerulonephritis
S. Agalactiae pathology
Neonatal disease
S. Dysgalactiae pathology
Pharyngitis
Acute glomerulonephritis
S. Pneumoniae pathology
Otitis media
Pneumonia
Sepsis, meningitis
Surface Proteins for S. pyogenes
Group specific:
Type specific:
Others:
Group specific: Lancefield Group A carbohydrate
Type specific: M proteins encoded by emm genes - epidemiologic markers
Others:
- M-like proteins
- hyaluronic acid capsule
- C5a peptidase
Proteins that mediate adherence to fibronectin
Lipoteichoic acid
F Protein
Avoidance of opsonization and phagocytosis
- Hyaluronic acid capsule
- M proteins block C3b binding
- M like proteins bind the Fc fragment of antibodies which reduces bound C3b
- C5a peptidase degrades C5a
Invasion of host cells
M protein and F protein
Toxins and Enzymes
Streptococcal pyogenic exotoxins SpeA, B, C and F - phage encoded, act as superantigens - Mediate cytokine storm Streptolysin S Streptolysin O Streptokinase Dnases
Spe toxins mediate what manifestations of S. pyogenes infections?
- Cytokine release may be key to the severity of necrotizing fascitis and toxic shock syndrome
- Responsible for rash in patients with scarlet fever
Streptolysin S
Oxygen and serum stable cell-bound hemolysin, responsible for complete lysis of red blood cells - kills macrophages and neutrophils
Sterptolysin O
Oxygen labile hemolysin
Streptokinase
Mediates cleavage of plasminogen, the release of plasmin and subsequent cleavage of fibrin and fibrinogen
Dnases
Depolymerize released DNA from lysed cells aiding spread of streptococci through infected tissues
Streptococcus Pyogenes: Patients with antibodies to ___ _______ are protected
M proteins
Streptococcus Epidemiology
- Transient colonizer of the oropharynx of healthy children and adults
- Spread by droplet transmission
- Pharyngitis affects children between 5 and 15 y
- Soft tissue infections by organisms introduced into superficial or deep tissues through a wound
Streptococcal pharyngitis
redness and edema of the mucous membranes, fever, pus, tonsilitis
Scarlet fever
Streptococcal pharyngitis and an erythematous punctiform rash due to the Spe toxins
Impetigo or pyoderma
Infection of the superficial layers of the skin in children - vesicles develop into pustules rupture and crust over
Erysipelas
Infection of the skin and subcutaneous tissues edema, induration with an distinct advancing border
Streptococcal toxic shock
Focal infection, bacteremia, shock hypotension, in conjugation with 2 or more of either ARDS, renal impariment, liver abnormality, coagulopathy, rash
Endocarditis
Streptococcal bacteremia allows access to normal, injured or congenitally deformed heart tissue
Necrotizing fasciitis
Infection of deeper subcutaneous tissues and fascia, extensive necrosis and gangrene
Rheumatic fever (Group A - late sequelae)
Follows respiratory infections, hypersensitivity response to streptococcal antigens
Glomerulonephritis (Group A - late sequelae)
Deposition of antigen-antibody complexes in the glomerular basement membrane
Streptococcus Pyogenes - Laboratory Diagnosis
Gram stain Antigen detection Nucleic acid amplification Culture (gram positive cocci in chains, catalase negative...) Antibodies to streptolysin O
Streptococcus, Prevention and control Pharyngitis: Penicillin allergic patients: Severe: Soft tissue:
Pharyngitis: Penicillin, penicillin V amoxicillin
Penicillin allergic patients: cephalosporin or macrolide
Severe: Penicillin IV + a protein synthesis inhibitor antibiotic
Soft Tissue: Surgical debridement and antibiotics
S. agalactiae - Group B
Physiology and structure:
Pathogenisis and immunity:
Epidemiology:
Physiology and structure: Expresses group B carbohydrate antigen
Pathogenisis and immunity: avoids phagocytosis by expressing a capsule
Epidemiology: Asymptomatic colonizatio of the lower gastrointestinal tract and genitourinary tract
S. agalactiae: Laboratory diagnosis
Treatment, Prevention and control
Gram stain of CSF for meningitis, pneumonia and wound infections
Treatment: drug of choice penicillin G for serious infections penicillin
Physiology and structure of S. pneumonia
Encapsulated Gram-positive, elongated or oval coccus arranged in pairs of chains
α-hemolytic colonies on blood agar
_______ ______ are the basis for the classification of S. Pneumonia strains
Capsular polysaccharides
S. Pneumonia - unique cell wall composition of phophorylcholine + species specific teichoic acids (2 types)
C polysaccharide - binds to serum
- C-reactive protein a marker for acute inflammation
F antigen - cross reacts with Forssman surface antigens on mammalian cells
S. Pneumonia pathogenseis
Colonization:
Resistance:
Inflammatory Response:
Colonization: Bacterial colonization is mediated by surface protein adhesins
Resistance: S. Pneumonia produces a secretory IgA protease that cleaves the Fc portion of IgA and prevents the association with host mucins
Inflammatory Response: Teichoic acids, peptidoglycan - activate complement pathways
S. Pneumonia - epidemiology
Transiently colonizes normal healthy individuals
Can occur when endogenous oral organisms are aspirated in to the lower airways
Disease = breakdown of natural defense mechanisms
In children - common cause of otitis media
Pneumococcal pneumonia
Replication of bacteria in the alveolar spaces
Abrupt onset, severe chill, sustained fever
Sinusitis and Otitis media
Infection of the paranasal sinuses and ear
______ occurs in 25-30% of patients with pneumonia and 80% of patients with meningitis
Bacteremia
S. Pneumonia laboratory diagnosis
Gram stain
Quellung reaction - detection of capsule with antibodies
ELISA
Culture
Isolate tested for bile solubility, should exhibit α-hemolysis on blood agar
S. Pneumonia treatment, prevention and control
Resistance:
Serious Infections:
- Many strains are now resistant to penicillin
- Resistance is documented for macrolides and cephalosporins
- Serious infections: Vancomycin + ceftriazone followed by monotherapy
Immunization: S. pneumonia
Adults and Children > 2 yrs:
Children < 2 yrs:
Adults and Children > 2 yrs: Immunize with vaccine containing 23 different capsular polysaccharides
Children < 2 yrs: Immunize with 13-valent conjugated vaccine
