Streptococci and Enterococci Flashcards
Are Streptococci catalase positive or negative?
Negative
What do Streptococci look like microscopically?
Gram positive cocci in pairs and chains
What are the different classifications of Strep based on hemolysis?
Beta-hemolytic = complete hemolysis Alpha-hemolytic = partial Gamma-hemolytic = non-hemolytic
What is the major species of Beta-hemolytic Group A streptococci?
Strep pyogenes
What is the major species of Beta-hemolytic Group B streptococci?
Strep agalactiae
What are virulence factors of Group A beta-hemolytic Strep?
- M protein
- Capsule
- Surface adhesins
- Toxins (hemolysins, SpeA,B,C)
- Enzymes (DNAses, hyaluronidase, streptokinase)
What is M protein?
- Antiphagocytic
- Binds serum proteins (e.g. Factor H) that inhibit activation of alternative complement components
- Elicits opsonic antibodies
- Adhesive
- Generates antibodies that react with cardiac myosin and sarcolemma (–> rheumatic heart disease)
What toxins are secreted by Group A Strep?
Hemolysins
- Streptolysin O (antibodies to this suggest previous infection)
- Streptolysin S
Streptococcal Pyrogenic Exotoxins (Spe)
- SpeA, Spe B, Spe C
What causes scarlet fever?
Spe A and Spe C (streptococcal pyrogenic exotoxins)
What causes Strep toxic shock syndrome?
Spe A and Spe C (streptococcal pyrogenic exotoxins)
What is the function of streptokinase?
Degrades fibrin
Used as a medication to break down large clots and restore blood flow, but must be used in very careful and controlled setting
What are suppurative (involving pus) diseases caused by Strep pyogenes (Group A beta-hemolytic strep)?
Pharyngitis - Scarlet fever Impetigo Erysipelas Cellulitis with lymphangitis Necrotizing fasciitis Streptococcal toxic shock syndrome
What are signs of bacterial pharyngitis?
No cough differentiates from viral a lot of the time
Fever
Purulent exudate
Cervical lymphadenopathy
Do rapid antigen tests have better specificity or sensitivity?
Better specificity.
Not as good sensitivity (false negatives)
What is the treatment of choice for Group A beta-hemolytic pharyngitis (strep throat)?
Penicillin
if penicillin allergy, use macrolides (azithro, clarithro, erythro) or clindamycin
What are symptoms of scarlet fever?
Rash on trunk
Strawberry tongue
Desquamation of skin
What is the treatment for impetigo?
Topical: bacitracin, mupirocin
Systemic: amoxicillin-clavulanic acid or cephalexin
What organisms can cause impetigo?
Group A Strep and Staph aureus
What is erysipelas?
Form of cellulitis, bright erythema, edema, sharp raised edges
What organisms can cause erysipelas?
High characteristic of beta-hemolytic Strep
What disorder do these clinical clues suggest:
- Pain out of proportion for clinical findings
- Septic shock in association with cellulitis
- Hemorrhagic bullae
Necrotizing fasciitis
What is the mechanism by which rheumatic fever/rheumatic heart disease develops?
Molecular mimicry - certain M proteins have epitopes shared with cardiac antigens
- T lymphocytes enter heart tissue –> inflammatory cytokines –> cardiac lesions
What is the mechanism by which acute glomerulonephritis develops from Strep?
Deposition of immune complexes
What are the clinical criteria necessary to diagnose rheumatic fever?
2 major criteria OR 1 major plus 2 minor criteria
Major: polyarithritis, carditis, chorea, erythema marginatum, subcutaneous nodules
Minor: arthralgia, fever, elevated C-reactive protein, 1st degree heart block
What population is at highest risk for Group B Strep?
Neonates (can acquire in utero, at birth, or first month of life)
What is treatment for Group B Strep?
Penicillin
- Need to screen all pregnant women and treat colonized women at term
What larger taxonomic group does Strep anginosis fall in?
Strep milleri
What are common clinical manifestations of Strep anginosis infection?
Cause abscesses (liver, brain, peridontal)
Is Strep anginosis alpha, beta, or gamma hemolytic?
Trick question! Can be all three
Are Viridans Strep alpha, beta, or gamma hemolytic?
Alpha and gamma
What clinical test/exam must be performed when a patient tests positive for Strep bovis?
Colonoscopy
S. bovis is associated with colonic neoplasia
What are common clinical manifestations of Viridans strep?
Endocarditis
Bacteremia
Abscesses
(really is only a problem if it gets into blood stream)
What is treatment for Viridans strep?
Penicillin or vancomycin (if resistant to penicillin)
What are the two major Enterococcus species?
E. faecalis, E. faecium
Is Strep pneumoniae alpha, beta, or gamma hemolytic?
Alpha hemolytic
How can we differentiate Strep pneumoniae from other alpha hemolytic Strep (like Viridans strep)?
Optochin disk on blood agar plate - Strep pneumo is susceptible
What are the virulence factors of Strep pneumoniae?
- Evades host immunity (capsule, pneumolysin)
- Adheres to host surfaces (phosphocholine, surface adhesion proteins)
- Produces very few toxins
What may often precede a Strep pneumoniae infection?
Viral infection
What are risk factors for Strep pneumoniae infection?
- Lack of pneumococcal vaccine
- Splenectomy
- Inability to form antibodies (e.g. multiple meyloma or HIV)
- Rare immune deficiencies
- Prior respiratory infection
- COPD, asthma, smoking
- Conditions that cause poorly functioning PMNs (alcoholism, diabeted, renal insuffiency)
What are the most common clinical presentations of Strep pneumoniae?
Otitis Sinusitis Bronchitis Pneumonia Meningitis Bacteremia
What are most common bacterial causes of otitis?
Strep pnemo and H. influenza
What are most common bacterial causes of meningitis?
Strep pneumo and Neisseria gonorrhea
(can differentiate since Neisseria will cause rash and Strep pneumo will also likely present in a second manner in addition to the meningitis)
What is the treatment for Strep pneumo meningitis?
Ceftriaxone and vancomycin
need vancomycin in case of penicillin resistance, usually start treatment immediately before culture results return
What is the treatment for Strep pneumo pneumonia?
Ceftriaxone and macrolide
What population is the Pneumovax vaccine for?
Adults over 65
What population is the Prevnar vaccine for?
All children
What biochemical test results indicate Enterococcus?
Catalase neg, PYR pos, LAP pos
What is the most important virulence property of Enterococcus?
Resistant to many antibiotics (during antibiotic treatment, other bugs get wiped out and enterococci are favored)
What is the treatment for E. faecalis?
Ampicillin (or vancomycin if penicillin resistant)
What is the treatment for E. faecalis endocarditis?
Ampicillin + an aminoglycoside
What is the treatment for E. faecium?
Vancomycin
What is the treatment for E. faecium endocarditis?
Vancomycin + an aminoglycoside
What is the treatment for E. faecium if it is VRE?
Linezolid or daptomycin
What are the common clinical presentations of Enterococci?
Bacteremia
Endocarditis
UTI
Intra-abdominal and pelvic infection
How would you differentiate Enterococcus central-line bacteremia and Enterococcus endocarditis?
Echocardiogram to test for endocarditis
What are peripheral signs of endocarditis?
Osler node - painful, finger tips
Janeway lesion - not painful
What population commonly is at risk for Enterococcal UTI?
Males with benign prostatic hypertrophy
If enterococcus comes back from wound culture, should you treat it?
No, unless from a deep or sterile culture
