Strep Flashcards
General description
Gram +
Facultative anaerobic
Cocci in pairs
Mostly commensal
3 schemes for identification
Hemolytic properties (alpha beta or gamma) - activity in blood agar
Lancefield groupings - serologic based on ex with antisera with cell wall carbohydrate antigens
Biochemical or physiologic properties
Further groups alpha
Alpha hemolytic strep
Shows incomplete lysis
Greenish discolouration
Beta hemolytic
Complete hemolysis
Gamma streptococci
Non hemolytic so no lysis
Under lancefield grouping A
Beta
GAS
Streptococcus pyogenes
Found in throats and skin
Pharyngitis cellulitis impetigo
Lancefield Group B
Beta
Strep agalactiae
Causes neonatal sepsis n meningitis
Found in female genital tract
Lancefield group D
Alpha
Enterococcus
Impetigo
Lesions
Start as vesicles and then rupture and release serum
Has to be distinguished from herpes
Lancefield C G
Beta hemolytic
Found in throat
Cause cellulitis (infx of dermis and subcutaneous tissue), bacteremia, endocarditis, pharyngitis
Strep pneumoniae
Alpha hemolytic
Found in throats
Causes pneumonia meningitis endocarditis corneal n conjunctival infx
Sequence of infection
Initial binding with surface binding proteins (lipotechoic n Fprotein)
Mediating internalization (w M protein - major virulence)
After internalization leads to
Persistence of infx - carrier state
Invasion of deeper tissues (aided by hyaluronidase)
M protein
Activates coagulation in bacterial surface
Major virulence protein
Class 1 or 2
Is a type of adhesive that mediatates internalization of GAS by host
Terminal part of amino chain is highly variable
Strains that don’t express M are avirulent
M protein is dominant in
Binding to keratinocytes on skin infx
Protein g binds to
Fav part of antibodies
Prevents opsonization
F protein
Binds fibronectin on host epithelial cell and favours adhesion
Critical in throats infx
Streptolysin O
Oxygen labile
Destroys rbc, WBC, and platelets
Allows for hemolytic ability
Pore forming toxin
Streptolysin S
Serum soluble
S means stable
Does beta hemolysis
Not antigenic
Streptodornase
DNAse enzyme that depolarizers DNA
Pyrogenic toxins
Found in few strains
Scarlett fever
Produce super antigens that stimulate T cell production to make streptococcal toxic shock syndrome
Streptokinase and streptodornase are used for
Enzymatic debridement is necrotic tissues
Gives antibiotics better access
Are fibrinolysis so break up fibrin blood clots
Pathology
Surface binding proteins bind epithelial fibronectin
Promotes high affinity binding and is first step in establishing infx
After adhering they invade cells
Host response to group a
- Complement coats strep
- B cells make type specific opsonic antibodies against M protein
(M is weakest link) - Antibodies bind
4.Fc receptors on neutrophils bind antibody and induce phagocytosis - Type specific antibodies can be detected 4-8 weeks after infx
Delayed antibody mediated diseases
Rheumatic fever
Glomerulonephritis
4 types of disease due to exotoxin release
Pharyngitis
Scarlet fever
Skin infx
Toxic shock syndrome
Strep pyogenes
Group a (GAS) Beta hemolytic
20-40% cases of pharyngitis in kids
1-4day incubation
Symptoms normal sickness
Tonsils or throats issue
Spread of GAS
Respiratory droplets
Short distance spread
Scarlet fever symptoms
Strawberry tongue
Circumoral pallor around lips
Upper respiratory infx
Step skin infx
Seen in poor hygiene conditions
Skin colonization plus trauma leads to impetigo
Lesions start as red papules eventually become honey comb like crusts
Erysipelas- bright red appearance of skin, forms plateau sharply demarcated from surrounding normal skin
Acute rheumatocnfever
Caused by GAS
Mitral valve is affected then aortic valve
Fever Myocarditis Joint swelling arthritis Chorea Subcutaneous nodules Rash
Deals with M protein of strep
Nephritogenic strain
Causes kidney damage
Get deposition of NaPlr in inner glomerular tuft
Causes endocapillary inflammation
Results in accumulation of immune complexes in outer side of glomerular tuft
Glomerulonephritis
Seen 1-2 weeks after infx
Inflammatory disease of glomeruli
Seen after skin infx
Deposits of m protein in glomerulus induces antibody response
Glomerulonephritis is characterized by
Edema
Hypertension
Hematuria
Proteinuria
Group B - beta hemolytic a
b for baby
Strep agalactiae
Part of normal vaginal flora
Common in first week after birth
Avoid immune response by
Polysaccharide capsule
Makes c5a peptidase which inactivated chemoattractant c5a
GBS manifestations
Neonatal sepsis, pneumonia, meningitis
Early onset infx occur within first week of life. High mortality rate
Late onset is 1week-3month
Get meningitis
Ophthalmia neonatrium
Conjunctivitis in the first month of life
Incident is 1.6-12%
