Streptococcal Flashcards
Catalase (-) GM (+) bacteria
Streptococcus and Enterococcus
Streptococcus characteristics
Gram (+) cocci. Facultative and capnophilic. Fastidious species
Hemolysis of Strep
Beta: complete. Alpha: partial. Gamma: none.
Color of hemolysis strep
Beta: yellow. Alpha:green. Gamma: white.
Group A Strep (GAS)
Only Strep. Pyogenes. Associated with pyogenic infections. Catalase (-). Pronounced beta hemolysis. Requires enriched medium
Epidemiology of S. pyogenes
Respiratory droplets. Crowding populations. Deaths usually due to post-infection complications.
Seasonal diseases of S. pyogenes
Pharyngitis in winter. Pyoderma in summer
Virulence factors in S. pyogenes
Capsule. LTA. M protein. M-like protein. F-protein.
Lipoteichoic Acid
Binds to epithelial cells. Accounts for 60% of adhesin
M protein
Adhesin. Antiphagocytic. Degrades C3b. Anchored in cell wall/extends to surface with variable sequenece at the distal end. Plasma fibrinogens binds to M-proteins, thus preventing complement activation/opsonization.
M-like protein
Binds IgG and IgM. Antiphagocytic
F protein
Mediates adherence to epithelial cells and internalization
Viral vs bacterial pharyngitis
Viral = 3Cs. Bacterial leads to abcess.
Non-suppurrative complications
Rheumatic fever: encapsulated and rich in M proteins.. Acture glomerulonephritis. Typically 1-3 weeks after acute pharyngitis.
Scarlet fever
GAS produces erythogenic toxins from lysogenic phi. Diffuse erythematous rash. Strawberry tongue. Rash will disappear in 5-7 days. Signals infaction by harmful GAS.
3 toxin types of S. pyrogenic
Exotoxins A, B, C
S. impetigo/pyoderma
more common in the summer. Skin colonization preceds clinical infection. Usually in face and legs (minor traumas get infected). S. aureus is main cause, strep pyogenes is second major cause.
Cellulitis
Infection involving skin and subQ.
Erysipelas
Form of cellulitis, aka butterfly rash.
Necrotizing Fascilitis
GAS responsible for 60%. Aka hemolytic strep gangrene. Involves deep fascia.
TSS and strep
Likely in pts w/ bacteremic GAS. (Always in NF pts). S. pyrogenic exotoxins act as super antigens. Resembles Staph TSS
Paricarditis causes in ARF/RHD
M proteins cause IgG to cross react with heart proteins. Antibiotic prophylaxis is needed.
Identification of S. Pyogenes
Beta hemolytic, catalase negative, bacitracin A disc sensitive
Only strep that gives a positive PYR test
S. Pyogenes
Strep. Agalactiae
Group B strep. Typical in woman urogenital track. Is a risk factor for postpartum sepsis. Babies can aquire it easily
Virulence factors of S. Agalactiae
9 capsular polysaccharide types.
Diseases of S. Agalactiae
Usually older/immunocompromised pts. UTI during/immediately after pregnancy. Puerperal sepsis**
Puerperal sepsis
Serious septicemia during or shortly after childbirth. More rare in developed countries
Identification of S. Agalactiae
CAMP test (98-100% positive) Bacitracin susceptibility (92% resistant)
CAMP test
Positive test is hemolysis where the 2 strains intersect (S. Agalactiae and S. Aureus)
Viridans Strep
Most produce a green pigment on blood agar. Prevalent in the oral cavity and URT.
Important Viridans Strep
Strep: Mitis Mutans Salivarius Sanguis
Disease states of viridans strep
Sub-acute endocarditis, meningitis, pneumonia. (Dental procedures with preexisting cardiac lesions)
Major cause of pneumonia in 1880s
S. Pneumoniae
Characteristics of S. Pneumoniae
Gram positive coccus Diplococci Fastidious (need blood/serum) Growth enhanced bby CO2 Causes alpha hemolysis on blood agar
Leading cause of bacterial sinusitis/middle ear infections
S. Pneumoniae
Virulence of S. Pneumoniae
Can colonized UR with surface adhesins. Produces sIgA protease and pneumolysin (Ply) that kills the ciliated epithelial cells/phagocytes. Lysis causes edema, hemorrhage, bacterial growth.
Capsule of S. Pneumoniae
Essential for virulence factor. Inhibits phagocytosis and complement pathways
Diseases associated with S. Pneumoniae
Co-inflection with influenza. Pneumonia, Meningitis, Otitis media, sub-acute endocarditis
Bacterial Pneumonia
Typically preceded by viral infection. High fever, productive cough, PMNs/lancet shaped diplococci, “rusty” sputum from blood leaks in capillaries. Usually lobar presentation (round in kids).
Otitis Media
Infection of middle ear/sinusitis. Leading cause of OM is S. Pneumoniae! Pain and fever very common.
3 most common causes of otitis media
S. Pneumoniae
Moraxella Catarrhalis
Haemophilus Influenzae
Bacterial Meningitis and S. Pneumoniae
CSF: purulent, high protein, low glucose.
Severe neurological defects in survivors
Most severe bacterial meningitis
Identification of S. Pneumonia
Catalase negative, bile soluble, optochin sensitive, susceptible to optochin (P disc). Can be tested for in urine. ELISA is 100% in CSF.
Enterococcus Characteristics
Gram positive, usually pairs or short chains. Resistant to bile**. High salt, highly antibiotic resistant (Vanco-VRE).
Epidemiology of Enterococcus
Nosocomial is very common. Typical in GI and gut.
Most common Enterococcus diseases
UTI* mainly nosocomial
Peritonitis (after surgery/abdominal trauma)
Endocarditis (persistent bacteremia)
Identification of Enterococcus
High salt/bile/temp
Do not lyse RBCs
Positive Pyr test
Anaerobic cocci
Part of normal flora of oral, GI tract, Genitourinary tract, skin. Susceptible to common antibiotics. Easily treated if identified as anaerobic cocci.
