Strep Pyogenes Flashcards
what are the group A streptococci?
strep pyogenes
is streptococcus catalase + or -?
it is catalase negative
will strep pyogenes be sensitive or resistant to bacitracin?
it will be sensitive
what are the 3 virulence factors for strep pyogenes?
M protein *
Streptolyin O*, streptolysin S
Streptococcal pyrogenic exotoxins (SPEs)
if cultivated on blood agar, it will cause what hemolysis?
beta-hemolytic
what does the M protein in strep pyogenes do?
- Mediates adherence to host cell
- Facilitates invasion of host cell
- Anti-phagocytic
- blocks binding of complement C3 to bacterial cell wall preventing phagocytosis
- Binds Fc portion of opsonizing antibodies preventing phagocytosis
what does Streptolysin O * do?
- Lyses RBCs, leukocytes, platelets
- It is Antigenic (stimulates antibody production)
how can streptolysin O be detected?
using ASO
what do streptokinases do?
- causes Lysis of clots and fibrin deposits *
- Facilitates spread of infection
what does C5a peptidase * do?
Degrades C5a reduced complement-mediated inflammation
what do the Streptococcal pyrogenic exotoxins (SPEs)* do?
- Cause the rash of scarlet fever
- Produced by Streptococcal TSS strains
- can be Superantigen *
- Interacts with both macrophages & T cells causing non-specific activation of T cells
- This results in release of large amts of cytokines (IL-1, IL-2 TNF-α)
what diseases does strep pyogenes cause?
phrayngitis (Strep Throat)
scarlet fever
skin and soft tissue infections
strep toxic shock syndrome
what is the most common cause of bacterial pharyngitis?
strep pyogenes
how is phrayngitis (strep throat) diagnosed?
how is the diagnosis confirmed?
rapid strep antigen test
confirmed on culture
can strep throat be left untreated and self-resolves? WHY?
NO! must treat with antibiotics
if left untreated may lead to rheumatic fever
what is this?
strep throat
what is this?
strep throat
what 2 complications can result from strep throat (strep pharyngits)?
Rheumatic fever and Scarlet Fever
what will cause the scarlet fever complication?
Group A strep producing pyrogenic exotoxin from strep pyogenes
how does scarlet fever present to in a clinic?
Erythematous rash *that starts in upper chest and spreads to extremeties
strawberry tongue
what is this?
what is this a consequence of?
who causes this?
erythemathous rash
scarlet fever
strep pyogenes
what is this?
strawberry tongue in scarlet fever
what skin and soft tissue infections does strep pyogenes cause?
impetigo
cellulatis
erysipelas
necrotizing fasciitis
what is this?
impetigo
impetigo looks like what other infection?
staph aureus
impetigo infection lesion is described as what?
honey-crusted lesions
what is erysipelas?
acute inflammation of the deep dermis and upper subcutis by strep
does erysipelas spread?
yes
what is the presentation for erysipelas?
lesions that present as hot, painful, red, raised
what will erysipelas lead to if left untreated?
respiratory tract or skin infection
what is this?
erysipelas
what is cellulitis?
what differentiates cellulitis from erysipelas?
Deeper infection than erysipelas
No clearly demarked separation between normal and infected skin
what is necrotizing fasciitis?
Bacteria spreads along superficial and deep fascial planes and enters following minor trauma, or hematogenous spread from Group A Strep throat infection to site of blunt trauma/muscle strain
what will necrotizing fasciitis cause?
extensive destruction of muscle and fat *
what is a major risk factor to developing necrotizing fasciitis?
History of recent varicella-zoster virus (VZV) infection
what is this?
necrotizing fasciitis
what strains of streptococci will cause strep toxic shock syndrome?
- prominent capsule and SPEs (pyrogenic exotoxin - superantigen) *
- M1 and M3 serotypes
- Preceding skin infection (eg cellulitis)
what will differentiate strep toxic shock syndrome from staph toxic shock syndrome?
Blood cultures positive for Strep pyogenes*, the bacteria will in the blood (bacteremia)
strep bacteremia usually follows what 2 diseases?
necrotizing fasciitis or toxic shock syndrome
what are the Non-suppurative Post-streptococcal sequelae? (complication from giving antibiotics)
Rheumatic fever
Acute glomerulonephritis
how do you diagnose rheumatic fever in a untreated strep throat?
positive serologic tests (ASO)*
will be negative for the bacteria in the throat or blood
why will rhumatic fever damage the heart, joints, skin andbrain?
Anti-streptococcal antibodies cross-react with tissues of the heart (mitral and aortic valves) *
what is rheumatic heart disease?
damage to the mitral and aortic valces (stenosis) 10-20 years after infection
what is acute glomerulonephritis?
what does it present with?
immune-complex disease
present with: hematuria, proteinuria, smoky/coal-colored urine
what has to happen to get glomerulonephritis strep pyogenes related?
Follows cutaneous infection, or pharyngitis *
how do you test for glomerulonephritis?
positive anti-DNAse B & ASO
What antibody tests do you use to verify rheumatic fever?
positive ASO for ARF *
What test do you use to differentiate strep pyogenes from staph aureus?
PYR test positive for strep pyogenes
how does strep pyogenes look under the microscope?
gram positive chains
how do you treat group A diseases?
penicillin
how do you treat pharyngitis by group A streptococcus?
oral penicillin/amoxicillin
what if patient is allergic to penicillin, and they are afflicted with strep throat?
erythromycin
how do you treat impetigo caused by strep A?
what about impetigo caused by staph aureus?
nafcillin
still use nafcillin
strep throat penicillin will prevent development of what disease?
rheumatic fever
what is DNases (streptodornases)?
why are they important?
- Depolymerize free DNA
- Antibodies to DNase B imp. marker for diagnosis of antecedent skin/throat infections *
