L16 Streptococcus Flashcards
Streptococcus Characteristics?
oval or spherical cocci, pairs or chains
small, grey to greyish-white colonies
Gram-positive
blood agar => hemolysis
catalase negative
Streptococci vs. Staphylococcus?
Streptococci:
Division in 1 plane =>pairs/ chains
Catalase Negative
Staphylococcus:
Division in multiple planes => irregular clusters
Catalase Postive
Classification of Streptococci?
Presence or absence of haemolysis around colonies growing on blood agar
Lancefield classification (of beta-hemolytic streptococci)
group-specific carbohydrate of cell wall => latex agglutination coats particles w/ antibody
20 Lancefield groups (A-H and K-V).
Classification of Streptococci based on presence or absence of haemolysis around colonies growing on blood agar
3 Streptococci of importance in human infection
Lancefield group?
Type of Haemolysis?
Streptococcus Pyogenes Description:
Colony characteristics?
Anaerobic/Aerobic?
Habitat?
Other?
Streptococcus Pyogenes Description:
–Gram-positive cocci in chains
–facultative anaerobes
–nasopharynx
–complete (beta) hemolysis
Virulence of Streptococcus Pyogenes?
M Protein Most important surface protein and virulence factor!!
- Antiphagocytic*: Opsonization prevents phagocytosis!! M protein binds factor H and fibrinogen impeding binding to bacterial surface
- Immunity ONLY against homologous serotype* (>80 serotypes): Type-specific opsonic antibodies against M protein responsible for immunity: Exposure to one M type DOES NOT confer immunity to other M types
Lipoteichoic Acid (LTA)
Protein F1(PrtF1) aka streptococcal fibronectin-binding proteins (sfbI)
Cell surface protein => adheres to fibronectin on respiratory epithelial cells
Capsule (MORE encapsulated = MORE virulent)
Antiphagocytic!!
composed of hyaluronic acid–chemically similar to human connective tissue
Aids adherence in pharynx: binds to CD44 on epithelial cells
Streptolysin O (SLO) and Streptolysin S (SLS)- pore-forming cytolysins, hemolytic and cytotoxic
SLO is antigenic: antibodies to SLO (ASOT) used in serodiagnosis
Streptococcal pyrogenic exotoxins (SPE)- Streptococcal toxic shock syndrome/Scarlet fever
Spreading Factors
Hyaluronidase-degrades hyaluronic acid
Deoxyribonucleases- hydrolyze nucleic acid and nucleoproteins
Streptokinase-converts plasminogen to plasmin-breaks down fibrin
Liquefies inflammatory exudates => spread through tissue planes
C5a peptidase
- degrades complement component C5a
- destroy C5a ability to act as chemo-attractant of leucocytes
=> when broken down, no inflammatory response
Role of M Protein for Streptococcus Pyogenes?
M Protein: Most important surface protein and virulence factor!!
Antiphagocytic:
Opsonization prevents phagocytosis!!
binding to factor H and fibrinogen impede binding to bacterial surface
Type-specific opsonic antibodies against M protein responsible for immunity:
Immunity ONLY against homologous serotype (>80 serotypes)
Exposure to one M type DOES NOT confer immunity to other M types
Clinical Manifestations of Strep Pyogenes?
•Acute pharyngitis/tonsillitis (most common cause)
•Scarlet fever
•Impetigo (crusted pussy lesions), erysipelas, cellulitis, sepsis in burns, Necrotizing fasciitis.
•Toxic Shock Syndrome
•Puerperal sepsis, endocarditis, pneumonia-post viral.
Non-suppurative post-streptococcal sequelae:
Acute Rheumatic Fever: Molecular mimicry
Antigenic similarity between somatic constituents of Group A Strep and human tissues (heart, synovium)
=> Cross-reactive antibodies react w/ heart and joint tissues
Type II hypersensitivity
Acute Glomerulonephritis
Immune complex containing a streptococcalantigen deposited in the affected glomeruli
Type III hypersensitivity
Non-suppurative post-streptococcal sequelae?
Acute Rheumatic Fever
Molecular mimicry
Antigenic similarity between somatic constituents of Group A Strep and human tissues (heart, synovium)
=> Cross-reactive antibodies react w/ heart and joint tissues
Type II hypersensitivityy
Acute Glomerulonephritis
Immune complex containing a streptococcalantigen deposited in the affected glomeruli
Type III hypersensitivity
Most common cause of pharyngitis/tonsillitis?
Streptococcus Pyogenes
Diagnosis of Streptococcus Pyogenes?
Pyrrolidinyl arylamidase (PYR) test most common
–S. pyogenes is PYR-positive
– Others negative
Lancefield grouping by latex agglutination.
Serological Diagnosis:
Antibodies to DNase B, hyaluronidase, NADase, and streptokinase
ASOT (Antibodies to Streptolysin O (SLO))
–peak 2-4 weeks after acute infection
–tonsillar-associated diseases
Streptococcus Pneumoniae description
Gram Pos/Neg?
Microbiological Characteristics?
Media?
Colony Characteristics?
Streptococcus Pneumoniae:
–Gram-positive
– pairs of ovoid or lanceolate cocci (diplococci)
–grow well on blood agar
Colonies:
Alpha hemolysis (greenish discoloration around colonies)
Optochin sensitive (Optochin disc, if no growth then optochin sensitive)
“draughtsman” appearance
Mucoid due to excessive capsular production
Streptococcus Pneumoniae virulence factors? (7)
Capsule: most significant virulence factor (Antiphagocytic) >90 capsular / serotypes with antigenic differences in polysaccharides
Choline-binding proteins
Pneumococcal surface proteins A (PspA) –binds to complement factor B** and prevents deposition of **C3b
Pneumococcal surface proteins C (PspC) –binds to complement factor H and prevents deposition of C3b
Pneumolysin–transmembrane pore-forming toxin, cytotoxic for phagocytic and respiratory epithelial cells
Autolysin: causes bacterial disintegration => release of cell wall components (peptidoglycan and teichoic acid)
Neuraminidase – contributes to adherence by cleaving sialic acid on mucous membrane surfaces
Epidemiology/Transmission of Streptococcus Pneumoniae
Epidemiology
- human only known reservoir
- nasopharynx
- Infections most common <2 and elderly
- transmission by droplets or contact with respiratory secretions
Contrasting features of Staphyloccoal and Streptococcal Toxic Shock Syndromes?
