Streptococcus pyogenes Flashcards
S. pyogenes
Morphology
Gr+ spherical cocci, chains
S. pyogenes
Diagnostic criteria
catalase -
beta hemolysis (blood agar)
Bacitracin susceptable
S. pyogenes
Pathogenicity
Lipoteichoic acids - adherence to fibronectin & epithelial
M & F proteins - invasion, interacting with host cell receptors
Hyaluronic acid capsule - indistinguishable from normal hyaluronic acid in mammalian CT –> poor immunogen –> decreased pahgocytosis = evasion
M proteins - block opsonization of C’ system’s C3b & C5a components - evasion
S. pyogenes
Enzymes (& immunigenicity)
- streptokinase
Cleave fibrin –> fibrinogen ==> lyses blood clots & fibrin deposits, facilitating rapid spread in infected tissues. Immunogenic = ABs formed against it: antistreptokinase ABs, useful in diagnostics. - Deoxyribonuclease
Depolymerize free deoxyribonucleic acid in pus –> reduced viscosity of abscess material –> facilitate spread of organism. DNase B is immunogenic –> production of anti-DNase B (an AB)
S. pyogenes
Toxins
Pyrogenic exotoxins
Superantigen –> cytokine storm. Toxin responsible for S. pyogenes’ more severe symptoms; necrotizing fascitis, streptococcal toxic shock syndrome & the rash in scarlet fever.
Hemolysins
- streptolysin S
Oxygen- & serum stable, lyses RBCs, leukocytes & platelets, non-immunogenic & beta hemolysis.
- Streptolysin O
Oxygen labile, lyses RBCs, leukocytes & platelets, immunogenic (ABs produced = antistreptolysin O, ASO), irreversibly inhibited by cholesterol in skin –> ASO ABs are not developed in cutaneous infections.
S. pyogenes
Streptococcal pharyngitis - incubation, symptoms, complication (+symptoms)
- 2-4days
- abrupt sore throat, fever, malaise, headache. Erythematous posterior pahrynx with exudate & cervical lymphadenopathy.
- Scarlet fever (pyrogenic exotoxin), 1-2days after initial clinical symptoms –> rash after 5-7days, upper chest & extremities but periorally pale, strawberry tongue, desquamation of rash’s superficial skin layer)
S. pyogenes
Streptococcal pyoderma/Impetigo - transmission, pathogensis
- direct contact with infected persons or fomities. Common in warm humid months in children. Coinfection is common with S. aureus.
- breakage of skin = introduction to subcutaneous tissue –> vesicles develop –> into postules –> rupture & scab
S. pyogenes
Erysepelas - symptoms & demographic
- localized pain & inflammation and lymph node enlargement & systemic signs (fever, chills & leaukocytosis). Raised infected area, distiguished borders
- young children/elderly, on legs, preceded by respiratory or skin S. pyogenes infection.
S. pyogenes
Streptococcal cellulitis - symptoms & characteristics
- Systemic & local inflammatory signs are visible.
- Skin & subcutaneous tissue with unclear borders between infected & healthy tissue.
S. pyogenes
Streptococcal necrotizing fascitis - characterized & pathogenesis
- deep in subcutaenous tissue, causing extensive destruction of muscle & fat. Introduction is often through breakage of skin.
- Spreads along fascia. Initially: cellulitis –> bullae formation + gangrene –> systemic symptoms –> toxicity, multiorgan failure & death
S. pyogenes
Streptococcal toxic shock syndrome - Cause, pathogenesis
- by other strep infections, due to overall toxic effects. Often co-develops with necrotizing fascitis & bacteremia
- initial local soft tissue inflammation –>pain & non-specific symptoms (fever, chills, malaise, nausea, vomiting & diarrhea) –> shock & organ failure (kidney, liver, heart & lungs).
S. pyogenes
Rheumatoid fever - characteristics, pathogenesis, location
- complication of strep inflammations (pharyngitis), 2-4weeks after initial infection
- M protein (T2 hypersensitivity) is alike human tissues –> autoimmune attacks by ABs
- heart, joints, blood vessels & subcutaneous tissues
S. pyogenes
Post-streptococcal glomerulonephritis - charactestics, mechanism, symptoms
- complication of strep (pyodermal or pharyngeal), 2 weeks later
- T3 hypersensitivity (depositions of immune complexes in glomerulus –> inflammation)
- acute inflammation of glomeruli –> dysfunction –> edema, hypertension, hematuria & proteinuria.
Streptococcus agalactiae
Streptococcus agalactiae - characteristics, virulence, demographic (+complications), transmission, prophylaxis
- beta hemolytic
- polysaccharide capsule (k AG)
- neworbs <3months old –> sepsis, pneumonia or meningitis
- vertical (intrauterine) or horizontal (mom/other children - child)
- screening & treatment of pregnant women with colonialization before labor
S. pyogenes
viridans streptococci - characteristcs, risk group, subgroups
- Alpha & gamma hemolysis (part of normal local microbiotas)
- immunosupressed, previously damaged heart valves
- mitis (endocarditis, sepsis if neutropenic, pneumonia & meningitis), mutans (dental caries & bacteremia) & salivarius (bacteremia & endocarditis)
