Streptococci Flashcards
How is streptococci classified?
Hemolysis and serologic specificity
What are the different hemolysis patterns?
Beta-hemolytic - complete hemolysis
Alpha - hemolytic - partial hemolysis
Gamma-hemolytic - no hemolysis
What are some general characteristics of streptococci?
Gram +
Non-motile
Catalase negative
Complex nutritional requirement
What are some characteristics of Streptococcal pyogenes?
Hyaluronate capsule
B-hemolytic
M-proteins (150 types)
What is the virulence factor of M proteins?
Inhibits opsonization by interfering binding of C3b and degrades C3b
What is streptolysin O?
Toxin produced by S. pyogenes
Lyses leukocytes, platelets, and erythrocytes
Immunogenic, indicating a recent GAS infection
What is streptolysin S?
Serum stable
Lyses leukocytes, platelets, and erythrocytes
Stimulates the release of lysosomal enzymes
B-hemolysis
nonimmunogenic
What is an important marker of cutaneous group A streptococcal infections?
Anti-DNase B
What is DNase?
Depolymerizes cell free DNA in pus; contributes to spread from local site
What is the function of streptokinase?
catalyzes activation of plasmin to lyse blood clots
What is pharyngitis?
Suppurative streptococcal disease (Strep Throat)
Exudates on tonsils
Children 5-15
What is Scarlet Fever?
Complication of Strep pharyngitis that occurs when the infecting strain is lysogenized by a bacteriophage that produces a pyrogenic exotoxin
Red maculopapular rash on trunk that spreads to extremities - intense at skin folds
Rash disappears within 5-7 days
What is Impetigo?
Streptococcal pyoderma cutaneous infection
Purulent with crusting
Colonization due to direct contact with an infected person or fomite
Young children, poor hygiene
What is Erysipelas?
Strep infection
Localized pain, inflammation, lymph node enlargement
Fiery red, advancing erythema - face or legs
Systemic signs - chills, fever and leukocytosis
All age groups
What is necrotizing fasciitis?
Rapidly spreading gangrene of skin and fascia
Streptococcal pyrogenic exotoxin released
Surgical debridement required
What are the two types of Necrotizing Fasciitis?
Type 1 - Polymicrobial, often anaerobes, occurs in diabetics, immunocompromised and post-surgery
Type 2 - Group A Strep, occurs in otherwise healthy people after skin injury
What is the classic case of Necrotizing Fasciitis?
Minor skin trauma with redness/warmth
Pain out of proportion to exam
Fever, hypotension
What is acute glomerular nephritis?
Acute inflammation of the renal glomeruli with edema, hypertension, hematuria and proteinuria
Can be post-skin or post-pharyngitis, caused by M protein
Nephritic syndrome 2-3 weeks after GAS infection
What is Acute Rheumatic Fever?
Post-pharyngitis Pancarditis (endo, peri, and myo)
Due to cross-reactivity of anti-M protein antibody with cardiac tissue (Type II autoimmune rxn)
Symptoms: migratory arthritis, subcutaneous nodules, carditis and eythema marginatum
What is the treatment for rheumatic fever?
Penicillin
What is PANDAS?
Post-streptococcal Autoimmune, Neuropsychiatric Disorders Associated with Streptococci
Used to describe a subset of children whose symptoms of OCD or tic disorders are exacerbated by GAS infection
What are some characteristics of Group B streptococcus?
G+
CAMP test positive
Hydrolyzes hippurate
B-hemolytic
Infects infants and colonizes vagina
What are some characteristics of Streptococcus pneumoniae?
G+
CAMP test negative
A-hemolyic (aerobically)
B-hemolytic (anaerobically)
Catalase negative
What are the virulence factors of S. pneumoniae?
Capsules
Biofilm formation
IgA proteases
Adhesins
Pneumolysin - destroys ciliated epithelial cell
What are four S. pneumoniae infections?
Lobar pneumonia
Meningitis
Sinusitis
Otitis media
How do you diagnose S. pneumoniae infections?
Gram stain
Quellung reaction - Polyvalent anti-capsular antibodies mixed with bacteria; increase refractive mass
Bile sensitive
Optochin sensitive
What are the clinically important T-independent antigens for B-cell activation?
Polysaccharides forming the thick capsules of pathogenic bacteria
E.g. S. pneumoniae, H. flu b, N. meningitidis
Where does T-independent B-cell activation occur?
Spleen marginal zone
Region between red and white pulp where marginal zone B cells reside
MZ B cells are more easily activated by antigens
What is the treatment for Strep infections?
Penicillin
Vancomycin w/ ceftriaxone (in the case of penicillin allergy)
What are the vaccines for strep infections?
PPSV-23 adult vaccine
PCV-13 - child vaccine as a four dose series
