Micro of Strep - Cross Flashcards
Generalized morphology of streptococci?
spherical gram (+) cocci in pairs or chains; catalase(-), varying hemolysis
Group A strep also known as?
Strep Pyogenes
Group B strep also known as?
Strep agalactiae
3 bugs in Group D strep?
Enterococcus faecalis, Enterococcus faecium, and Strep bovis (gallolyticus)
Diagnosis of GAS?
Do a rapid swab and a culture at time of presentation
Diseases that GAS most commonly causes?
Pharyngitis (most common cause), cellulitis/impetigo, necrotizing fasciitis, TSS, scarlet fever, rheumatic fever, glomerulonephritis
GAS virulence factors (there are 9)
1) Hyaluronidase 2) Streptokinase 3) DNase 4) C5a peptidase 5) Streptococcal chemokine protease 6) Steptolysin O 7) Strepolsyin S 8) Protein M 9) Polysaccharide capsule
Action of Hyaluronidase
Degrades hyaluronic acid in the subQ tissue; known as spreading factor, facilitates cellulitis/skin infection
GAS pyogenes
Action of Streptokinase
Plasminogen–>Plasmin; role in infection unclear
GAS pyogenes
Action of DNase
Degrades DNA exudate to prevent bacteria from being trapped in neutrophil extracellular traps (NETs)
GAS pyogenes
Action of C5a peptidase
Cleaves C5a; significantly impedes influx of neutrophils early in infection
GAS pyogenes
Action of Streptococcal chemokine protease
Prevents migration of neutrophils to infection site by degrading IL-8
GAS pyogenes
Action of Streptolysin O
cytotoxic, protects GAS from phagocytic killing
Strepolysin O hemolysis characteristics (on agar)
Oxygen labile, beta hemolysis only when UNDER the surface of blood agar
GAS pyogenes
Streptolysin S hemolysis characteristics (on agar)
Oxygen stable, beta hemolysis ON THE SURFACE of blood agar
GAS pyogens
2 distinguishing physical exam findings/symptomology of GAS phraygnitis
Tender, enlarged cervical lymph nodes and ABSENCE of uri symptoms (cough, rhinorrhea)
Specificity/Sensitivity of GAS rapid screen?
High specificity, low sensitivity (false negatives common)
Typical course of GAS pharyngitis abx?
10 days, patient must finish the abx
Why do you treat GAS pharygnitis? Most cases are self limiting
To prevent complications; Rheumatic fever, otitis media, mastoiditis, meningitis, retropharyngeal abscess
What type of GAS illness does rheumatic fever follow?
Only follows a pharyngitis
How does mastoiditis normally occur?
Due to an untreated otitis media and subsequent local spread
What is erysipelas?
A rapidly spreading, erythematous cutaneous swelling on the face. Sometimes in a butterfly distribution
Contrast necrotizing fasciits vs. cellulitis?
The necrotizing fasciitis won’t look that bad on physical exam; cellulits looks erythematous, swollen, etc.
Physical exam finding on necrotizing fasciitis (this is on the test)?
PAIN OUT OF PROPORTION TO EXAM
Difference in diagnosis of toxic shock with S. aureus vs. GAS?
S. aureus doesn’t require isolation of bactria; for GAS, you must isolate bacteria from a normally sterile site (blood, CSF, etc)