Streptococcus Flashcards by Fred Jones-Rosa

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)

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Classification of Streptococci

1) Cell wall carbohydrate antigens recognized by specific antibodies
2) Hemolytic pattern on agar containing blood cells
3) Biochemical properties

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Hemolytic Pattern on agar containing blood cells

Alpha - partial hemolysis or “greening”
Beta - Complete clearing
Gamma - no change in red blood cells

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Lancefield typing can recognize…

Group A Streptococci = S. pyogenes
Group B Streptococci = S. agalactiae
Group C = S. Dysgalactiae
Group F = S. Anginosus

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S. Pyogenes pathology

Pharyngitis
Skin and soft tissue infections
Rheumatic fever
Glomerulonephritis

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S. Agalactiae pathology

Neonatal disease

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S. Dysgalactiae pathology

Pharyngitis

Acute glomerulonephritis

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S. Pneumoniae pathology

Otitis media
Pneumonia
Sepsis, meningitis

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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

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Proteins that mediate adherence to fibronectin

Lipoteichoic acid

F Protein

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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

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Invasion of host cells

M protein and F protein

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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

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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

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Streptolysin S

Oxygen and serum stable cell-bound hemolysin, responsible for complete lysis of red blood cells - kills macrophages and neutrophils

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Sterptolysin O

Oxygen labile hemolysin

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Streptokinase

Mediates cleavage of plasminogen, the release of plasmin and subsequent cleavage of fibrin and fibrinogen

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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