Streptococci Flashcards
What is Group A Strep?
Mostly Streptococcus pyogenes

What diseases can GAS cause?
–Pharyngitis (leading bacterial cause)
–Cellulitis/impetigo/erysipelas
–Necrotizing fasciitis
–TSS
–Scarlet fever
–Puerperal sepsis
–Endometritis
–Rheumatic fever
–Glomerulonephritis
RESPECT PING
How is GAS transmitted?
Most strep are part of normal flora (found on skin and oropharynx)
T or F. Strep pyogenes is bacitracin sensitive
T.
What are the main virulence determinants of GAS?
- Polysaccharide capsule
- Hyaluronidase
- Streptokinase
- DNase (streptodornase)
- C5a peptidase
- Streptococcal chemokine protease
- Streptolysin O/S
How does the Polysaccharide capsule promote its virulence?
It is anti-phagocytic and Abs are not formed against capsule because hyaluronic acid is normal component of body and humans are tolerant to it.
What is the main antigen of human immune response against GAS?
M-protein
What does Hyaluronidase do?
degrades hyaluronic acid (in subcu tissue);
–known as spreading factor – facilitates spread of GAS in cellulitis/other skin infections
What does streptokinase do?
activates plasminogen to form plasmin which dissolves fibrin in clots, thrombi and emboli. Role in GAS infections unclear
What is the effect of DNase (streptodornase)?
It degrades DNA in exudates/necrotic tissue. Protect the bacteria from being trapped in neutrophil extracellular traps (NETs).
What is the effect of GAS having C5a peptidase?
It cleaves C5a produces by the complement system. Minimizes influx of neutrophils early in infection
What is the effect of Streptococcal chemokine protease?
prevents migration of neutrophils into site of infection by degrading chemokine IL-8 which would recruit neutrophils to site
What is the role of SLO?
It is cytotoxic and protects GAS from phagocytic killing
•Hemolysin. Oxygen labile. Causes beta hemolysis only when colonies grow under the surface of the blood agar plate.
What is the role of SLS?
–More modest effect on virulence.
•Hemolysin. Oxygen stable. Causes beta hemolysis on the surface of the plate
How does this disease present?

Pharyngitis presents as inflamed tonsils with pharygneal exudate with systemic symptoms of sore throat, fever, N/V, and enlarged cervical lymph nodes
symptoms of URI absent
How is GAS pharyngitis diagnosed?
–Rapid strep antigen test available in 10 minutes
–If rapid antigen test is negative but suspicion is high, do a throat culture
How does the pharygnitis GAS rapid antigen test work?
If positive, it causes agglutination of AB bound to latex particles using antigens extracted from a throat swab
highly specific, but low sensitivity
How is GAS treated?
•If there is clinical suspicion, do not delay treatment
–Oral Penicillin V 500 mg 2-3 times daily x 10 days
–Amoxicillin 500 mg BID x 10 days
–Cephalexin 500 mg BID x 10 days
If culture is negative, therapy should be discontinued.
How can you treat GAS if the patient is allergic to penicillin?
–Azithromycin 500 mg x 1 followed by 250 mg daily on days 2-5
–Clarithromycin 250 mg BID x 10 days
–Clindamycin 600 mg TID x 10 days
What are possible sequelae of untreated GAS?
- Otitis media
- Sinusitis
- Mastoiditis
- Meningitis
- Peritonsillar/retropharyngeal abscess
- Rheumatic fever
What is this?

Erysipelas- a complication of GAS infection characterized by rapidly spreading erythematous cutaneous swelling that may begin on the face or, less frequently, on the body or an extremity. The rash has a sharp, well-demarcated, serpiginous border and may form a “butterfly” distribution on the face.
What is this?

cellulitis- a complication of GAS infection
What is this?

Impetigo- a complication of GAS that is characterized by lesions that begin as papules progressing to vesicles then pustules that rapidly break down to form adherent crusts with golden appearance
What is this?

GAS necrotizing fasciitis
























