GROUP A STREPTOCOCCI Flashcards
TRUE OR FALSE:
Group A streptococci is NOT part of the normal flora.
TRUE. It is pathogenic to man.
MOT:
contaminated droplet
“Fever producing bacteria”; flesh eating bacteria:
S. pyogenes
Microscopy of S. pyogenes:
gram-positive cocci in chains
Culture of S. pyogenes:
small, translucent and smooth; well-defined B-hemolysis
Cultivation media:
- BAP: beta-hemolytic
- Columbia agar with Colistin and Nalidixic acid (CNA)
Will inhibit gram-negative organisms, staphylococci, Bacillus spp., & coryneform:
CNA
Major virulence factor; antiphagocytic:
M protein
Not present in any other Lancefield groups:
M protein
Inhibits the activation of complement:
M protein
Associated with rheumatic fever:
Class I M protein
Associated with glomerulonephritis:
Class II M protein
Mediates epithelial cell attachement:
protein F
Bacterial adherence to the respiratory epithelium:
lipoteichoic acid
Weakly immunogenic; prevents opsonized phagocytosis; masks its antigens:
hyaluronic acid capsule
Causes the lysis of fibrin clots:
streptokinase
A protein that binds to plasminogen and activates the production of plasmin:
streptokinase
“Oxygen-labile”; highly antigenic:
streptolysin O
Responsible for subsurface hemolysis on BAP incubated ANAEROBICALLY:
streptolysin O
Causes lysis of WBCs, platelets, tissue cells; induces antibody response:
streptolysin O
Streptolysin O is inhibited by:
cholesterol in skin lipids
Detects recent infection with S. pyogenes:
Anti-streptolysin O test
Detect antibodies to the streptolysin O enzyme produced by group A streptococcus, which is able to lyse RBCs:
Anti-streptolysin O test
The most diagnostically important antibodies:
“HAD”
Anti-hyaluronidase
Anti-ASO
Anti-DNAse B
“Oxygen-stable”; nonantigenic:
streptolysin S
Responsible for subsurface hemolysis on BAP incubated AEROBICALLY:
streptolysin S
Causes lysis of WBCs:
streptolysin S
Provides more mobility to the pathogen:
deoxyribonucleases (DNAse)
Inactivates the chemotactic factor for neutrophils and monocytes:
C5 peptidase
It solubilizes the ground substance of mammalian tissue to separate the tissue and spread the organism:
hyaluronidase (spreading-factor enzyme)
Act as superantigens activating macrophages and T-helper cells, and induces the release of powerful immune mediators:
Streptococcal pyrogenic exotoxins (SPEs)
SPEs are formerly known as:
erythrogenic toxins
Mediates rash in scarlet fever:
SPEs
“Strep throat”
pharyngitis or tonsilitis
Diagnosis of pharyngitis:
throat culture or direct antigen detection
A punctuate exanthem overlying diffuse erythema and appears initially on the neck and upper chest:
scarlet fever (scarlatina)
It results from a throat infection with a strain of S. pyogenes that carries a lysogenic bacteriophage(T12):
scarlet fever
Cardinal signs of Scarlet fever:
- diffused red rash from the chest to the extremities
- “strawberry colored” tongue
Susceptibility test for scarlet fever:
Dick’s test (erythrogenic toxin)
Dick’s test (+) result:
erythema or redness of the sites
Diagnostic test for scarlet fever (current infection):
Schultz Charlton (anti-erythrogenic toxin)
Schultz Charlton (+) result:
“blanching phenomenon” - rash fades
Skin infection characterized by a defined area of redness (erythema) and accumulation of fluid (edema):
cellulitis
Skin infection characterized by painful reddish patches that enlarges and thicken with a sharply defined edges:
erysipelas
“Galloping gangrene or flesh-eating bacteria syndrome”
necrotizing fasciitis
Categories of necrotizing fasciitis:
Types:
1: mixed infection caused by both anaerobic and aerobic species
2: consists only of group A streptococci
3: gas gangrene and clostridial myonecrosis
Characterized by fever, inflammation of the heart, joints, and blood vessels:
rheumatic fever
Inflammatory disease of the renal glomeruli; results from the deposition of antigen-antibody complexes:
acute glomerulonephritis or Bright’s disease
Condition in which the entire organ system shuts down, leading to death:
streptococcal TSS
Plays a major role in the pathogenesis of streptococcal TSS:
Spe A
Specimen on choice:
pharynx and tonsillar swabs (throat swab)
Used to differentiate S. pyogenes from other B-hemolytic group:
bacitracin disk test/taxo A
Helpful in the screening for Group A streptococci in throat cultures:
bacitracin disk test
Bacitracin disk test (+) result:
any zone of inhibition (susceptible)
Organism also susceptible (+) to bacitracin:
Group C and G
Sulfamethoxazole and Trimethoprim (SXT) test (+) result:
resistant (Group A and B)
SXT test (-) result:
susceptible (Group C)
Detects the presence of PYRase or pyrolidonyl-arylamidase enzyme:
PYR test
The only B-hemolytic streptococci that is PYR (+):
S. pyogenes
PYR test (+) result:
bright/cherry red color (B-naphthylamide) upon adding 0.01% of cinnamaldehyde reagent (p-dimethyl-aminocinnamaldehyde)
PYR test (-) result:
no color change
Other PYR test (+) organism:
“GAE”
Gemella
Aerococcus
Enterococcus
Drug of choice:
Penicillin, Erythromycin
