Streptococci Flashcards
Nutritional requirement
Complex, need blood or serum enrich media for isolation
group A
S. Pyogeny
G+ Facultative anaerobe Capsule (HA) Beta-hemolytic on blood agar M protein F protein bind fibronectin - helps establish infection
Difference between Streptolysin O and S
O is immunogenic
What contributes to spread of free dna from local site
DNase
Important marker of cutaneous group A streptococcal infections
Anti-DNase B
Function of streptokinase
Catalyzes activation of plasmin to lyse blood clots
Suppurating Streptococcal Disease
Pharyngitis Scarlet fever Skin infection: impetigo, purulent with crusting Cellulitis Erysipelas Necrotizing Faciitis
Nonsuppurative Streptococcal Disease
Acute glomerular nephritis
No GAS present
After pharyngitis or skin infection
Symptoms: facial edema, blood in urine (smoky urine)
AGN is due to
Immune complex deposition on the glomerular basement membrane
Acute Rheumatic Fever (ARF)
No GAS present
After pharyngitis only
Symptoms: migratory arthritis, subcutaneous nodules, carditis and erythema marginatum
May proceed to rheumatic fever
ARF is due to
Cross reactivity of anti-M protein antibody with human cardiac tissue
Sources of GAS
Normal flora of skin
Oropharynx
GAS causes infection upon ______ of _______
Transmission
Upon penetration of tissue
Person to person
What test is used in RF for Ab detection?
GAS
ASO test
Ag detection?
GAS
Throat swabs
Treatment
GAS
Penicillin
Oxacillin or vancomycin in mixed culture
Culture
GAS
Blood agar
Specialized selective agar
What is GAS sensitive to?
Bacitracin
GBS
which test differentiates a. Galactiae from other streps?
CAMP +
Increased zone of hemolysis
CAMP factor produced by GBS that enhances beta-hemolysis of S. Aureus
Clinical problems associated with GBS
Threat to infants infected perinatally (meningitis, bacteremia (sepsis), pneumonia)
Post-partum endometritis, esp after C section
GBS
Source
Transmission
Normal flora of GI and Vagina
Vertical transmission: either at birth or via ascension in utero
GBS
Virulence factors
Capsule (resist phagocytosis) Sialic acid (inhibits alternate pathway of complement)
Which is Bacitracin resistant?
GBS
Treatment for GBS
Penicillin G
Alone or in combination with Aminoglycosides
Passive immunizations
Groups C and G
Non rheumatic
Otherwise like group A
Viridans Streptococci
Normal flora of mouth and teeth
Alpha hemolytic
Resistant to optochin
Sub-acute endocarditis
Central role in dental carries
No Lancefield antigens
Treatment of streptococcal endocarditis
Penicillin and antibiotic prophylaxis
Streptococcus pneumoniae (SP)
Alpha or beta hemolytic?
Alpha - aerobically
Beta - anaerobically
SP - bile solubility ?
Positive
What disease is SP resistant ?
Chronic granulomatous disease
Two distinct characteristics of Streptococcus:
- non motile
- catalase negative
Virulence factors for SP
Capsules
Biofilm
IgA protease (IgA –> Fab and Fc fragments. Prevents opsonization)
Adhesins
Pneumolysin (destroys the ciliated epithelial cell)
SP infections:
Lobar pneumonia (esp sickle cell disease)
Meningitis
Sinusitis
Otitis media
Diagnosis of SP:
Quelling rxn - polyvalent anti-capsular Ab are mixed with the bacteria – inc in refractive mass around the bacteria
Bile / optochin sensitive
Treatment of SP:
Penicillin G
Vancomycin (if P allergy)
Vaccines for over 60 and compromised host
Enterococcus
Normal flora of large bowel and feces
Antibiotic resistance common
Nosocomial infection
Virulence factors for Enterococci :
Aggregation substance and carbohydrate adhesins: helps in colonization
Cytolysin
Gelatinase
Antibiotic resistance: resistant to aminoglycosides, beta-lactams, vancomycin
Cytolysin
Inhibit G+ bacteria and induce local tissue damage
Enterococci diagnosis:
Resistant to optochin
Doesnt dissolve when exposed to bile
Treatment of Enterococci
Ampicillin
Combo of Aminoglycoside and vancomycin for resistant strain
Which AA seq does Vancomycin resistant Enterococci have a substitute for?
D-Ala-D-Ala
Target for vancomycin
