Streptococci Flashcards
Most frequent cause of pharyngitis
GAS - strep pyogenes
GAS pharyngitis diagnosis
rapid antigen test - High specificity, low sensitivity
oxygen labile. Causes beta-hemolysis only when colonies grow under surface of blood agar plate
Streptolysin O
oxygen stable. Causes beta-hemolysis on surface of plate.
Streptolysin S
alpha hemolysis - green
Viridans group Strep
S. pneumoniae
beta hemolysis
GAS
GBS
GCS/GGS
Protudes from outer surface of cell and interferes with ingestion by phagocytes, 80 serotypes
M protein (GAS)
Polysaccharide capsule made of? GAS
Hyaluronic acid - antiphagocytic
facilitates spread of GAS in cellulitis/other skin infections
Hyaluronidase
activates plasminogen to form plasmin dissolves fibrin in clots, thrombi and emboli
Streptokinase -GAS
degrades DNA in exudates/necrotic tissue. Protect the bacteria from being trapped inneutrophil extracellular traps (NETs).
DNase (streptodornase) -GAS
cleaves C5a produces by the complement system. Minimizes influx of neutrophils early in infection.
C5a peptidase
prevents migration of neutrophils into site of infection by degrading chemokine IL-8 which would recruit neutrophils to site
Streptococcal chemokine protease
Untreated GAS pharyngitis complications
Otitis media Sinusitis Mastoiditis Meningitis Peritonsillar/retropharyngeal abscess Rheumatic fever - Immune mediated
GAS Tx
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
GAS Tx in Pen allergy pt
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
cellulitis, impetigo, erysipelas
GAS soft tissue infections
responsible for rash of scarlet fever. Acts as superantigen
Erythrogenic toxin - GAS
causes most cases of TSS. Superantigen – causes release of large amounts of cytokines
Pyrogenic exotoxin A - GAS
protease that rapidly destroys tissue and is produced in large amounts by the “flesh-eating” strains of GAS that cause necrotizing fasciitis
Exotoxin B - GAS
Diagnosis of TSS from GAS
includes isolation of GAS from normally sterile site (blood, CSF, tissue biopsy) and hypotension plus other organ involvement
Tx Strep TSS
Penicillin plus Clindamycin
More frequent after skin infections than pharyngitis
Ag-ab complexes on glomerular basement membrane
Post-strep glomerulonephritis
HTN, facial edema, LE edema, dark urine due to RBCs
Many cases are subclinical
It is unclear if early treatment of the infection can prevent this complication
Post-strep glomerulonephritis
2 weeks after GAS pharyngitis
Acute Rheumatic Fever
Jones criteria
Joints: polyarthritis (affects several joints in quick succession)
Carditis (pancarditis, aortic/mitral valves also affected)
Nodules (subcutaneous) (firm painless lesions up to 2 cm in size)
Erythema marginatum (evanescent, pink rash involving trunk most often
Sydenham chorea (neurologic disorder consisting of abrupt involuntary movements)
ASO titer to aid dx
Anaerobe, Members of normal flora of gut, mouth, female genital tract
Peptostreptococcus - Tx with penicillin
Janeway lesions, Osler’s nodes (subacute, painful, violaceous), and Roth spots
Indicative of Infective Endocarditis
exudative, edematous hemorrhagic lesions of the retina
roth spots
Endocarditis _____ fatal if not treated. 3 sets of blood cultures needed esp in subacute cases to get a positive
100%
Hydrolyze esculin in presence of bile (produce black pigment on bile-esculin agar)
Group D Strep - Enterococcus faecalis/faecium, Strep Bovis, e.g.
VRE: more likely
Enterococcus faecium.
Linezolid or Daptomycin used for treatment in these infections
Causes endocarditis in patients with colon cancer. Very strong association.
Will not grow in hypertonic saline
Treatment: PCN, Ceftriaxone, or Vancomycin
Strep Bovis
Can grow in hypertonic saline or in bile.
Enterococcus faecalis/faecium
Cause hospital-acquired UTIs, blood stream infections (many times line-related) and endocarditis
Enterococcus faecalis/faecium
Narrow zone of beta hemolysis
Lack of hydrolysis of bile esculin agar
Hydrolyzes hippurate
Streptococcus agalactiae (GBS)
Bacitracin resistant (GAS is bacitracin sensitive) CAMP test: protein is produced that enhances hemolysis on sheep blood agar when combined with beta-hemolysin of S. aureus
Streptococcus agalactiae (GBS)
Causes neonatal sepsis, meningitis, PNA
Main risk factor: PROM in women colonized; also babies born prior to 37 weeks; children whose mothers lack antibodies
Streptococcus agalactiae (GBS)
important cause of invasive infections such as septic arthritis, cellulitis, osteomyelitis
Strep agalactiae (GBS) Diabetes main predisposing factor, also breast cancer
Streptococcus agalactiae (GBS) Tx
Penicillin/ampicillin (Vanc if allergic)
Most common cause of subacute bacterial endocarditis
Strep viridans group
How can viridans group strep be distinguished from S. pneumoniae?
Resistant to lysis by bile Optochin resistant (strep pneumo is opto sensitive)
Cause of dental caries. Synthesizes polysaccharides in dental plaque
Strep mutans
