Streptococci Flashcards
What happens in alpha hemolysis?
erythocytes NOT destroyed; greenish discoloration
What happens in beta hemolysis?
erythrocytes ARE destroyed; clearing underneath growth
What happens in gamma hemolysis?
non-hemolytic; anything that’s not alpha or beta
What’s the basis of lancefield classification?
C-carbohydrates and glycerol teichoic acid
What are the classifcations of Strep?
Group A = S. pyogenes
Group B = S. agalactiae
Group D = E. faecalis
*strep pneumoniae and viridans= NONE
What hemoylitic pattern is seen in Strep Pneuomoniae and Strep Viridans?
Pneumoniae = alpha/beta/none
Viridans=alpha
What are some characteristics of Strep Pyogenes?
- transient flora
- not always symptomatic
- not common to culture
What is the mode of transmission for Strep Pyogenes?
- from asymptomatic carriers via respiratory droplets and skin-to-skin
- via fomites and insect vectors
- for soft tissue infections, breakage in skin
What are GAS virulence factors?
- fibronectin binding proteins
- M protein: binds fibronectin and fibrinogen -> antiphagocytic
- toxins: Streptococcal Shock Syndrome
- capsule: antiphagocytic and anti-Ig
- DNAases: pus that’s less viscous than Staph Aureus
What’s the difference between the pus of Staph Aureus vs Strep Pyogenes?
GAS has a more liquefying pus
When do we do a rapid strep test?
need 2, 3, or 4 criteria of: tonsilar exudates, tender cervical adenopathy, absence of cough, fever
if positive: treat with antibiotics
if negative: back to square one
When do we not do rapid strep test?
patients with history of RF, vascular heart disease, immunosuppression, recurrent/chronic pharyngitis
Define cellulitis.
diffuse inflammation of CT that spread along the fascial planes
often occuring where skin has previously broken
What layers do erysipelas infect?
superficial infections of dermis and upper subcutaneous layer (have well defined edge)
How do we treat the skin infections related to Strep Pyogenes? (impetigo, cellulitis, erysipelas)
antibiotics!
What are the streptococcal pyrogenic exotoxins?
superantigens (cytokine storm)= interacting with macrophages & helper T cells to release IL-1, IL-2, IL-6, TNF-alpha, TNK-beta, and gamma-IFN
SpeA and SpeC = encoded by lysogenic phages
SpeB = located in bacterial chromosome (found in all GAS)
What’s the treatment for necrotizing fascititis?
surgical removal of all the affected areas + empiric antibiotics like vancomycin
What is special about the M protein?
shares same epitopes as heart muscles (molecular mimcry) -> so when make Abs to M protein, may make Abs to heart muscles too
What are the theories for post-streptococcal glomerulonephritis?
- IgG-streptococcal antigen complexes depositing on glomerular tissue
- cross-reactivity between unidentified streptococcal Ags and glomerular membrane components
- deposition of nephrostreptokinase-plasmin complexes on glomerular basement membrane and subsequent damage by host plasmin
What should be done to prevent spread from S. Agalactiae positive mother to neonate?
prophylactic antibiotics for positive MOM to decrease colony size and reduce risk of transmisson
What is virulence factor for S. Agalactiae that’s important for preventing phagocytosis?
capsule
Type II: adult disease
Type III: infant disease
What’s the clinical presentations for early onset GBS?
symptoms within day 0-1
respiratory distress, apnea, sepsis (bacteremia is most common form), pneumonia, meningitis
What treatment can be utilized for the severe cases of early onset GBS?
extracorporeal membrane oxygenation (ECMO): temporizing, supportive treatment to effectively bypass severely diseased lungs while they’re given time to heal from infection
What group have a higher proportion of maternal colonization?
African Americans and nonsmokers
What’s significant of maternal GBS colonization?
- colonized asymptomatically that comes and goes over months
- NOT STDs!! develops over time
- bacteria actually live in GI tract but can spread to genital tract
- colonization is not altered by or dependent on pregnancy
What are some risk factors for early-onset GBS?
- obstetric: preterm delivery (<37weeks), prolonged rupture of membanes, infection of placental tissues or amniotic fluid (fever during labor)
- detectable GBS in mother’s urine (marker for heavy colonization)
- previous infant with GBS
- low maternal levels of anti-GBS Abs
- AA, young maternal age
What test follows hemolysis test for GBS?
latex agglutination test for confirmation
What’s the main virulence factor that prevents phagocytosis of Strep Pneumoniae?
capsule (forms halo on culture)
What is another important virulence factor for Strep Pneumoniae?
pneumolysin (exo-enzyme)- leads to rusty sputum
How is Strep Pneumoniae transmitted?
respiratory
What’s the pathogenesis of Strep Pneumoniae?
- bacteria colonize epithelial cells and pumps out toxins
- capsule facilitates invasiveness
What are some predisposing factors for Strep Pneumoniae infection not covered on sketchy?
alcoholism, anesthesia, and previous infection
What antibiotics is used for treatment of strep pneumo?
levofloxacin (quinolone) and ceftriaxone
Is there a vaccine for Strep Pneumo?
yes, two carbohydrate capsule (use on at risk individuals)
- pneumococcal polysaccharide vaccines, PPSV14/PPSV23/Pneumovax (Merck) Pnu-Imune 23 (Wyeth)
- pneumococcal conjugate (diphtheria CRM107 protein) vaccines, Prevnar PCV7/PCV13
What’s the pathogenesis for S. pneumococcal meningitis?
- adheres and colonizes nasopharynx
- IgA1 protease protects from host Ab
- once in bloodstream, capsule helps evade opsonization
- enters CSF through receptors on endothelial surface of BBB
What’s phase variation?
S. pneumoniae being able to change constituition of its capsule
How do we treat otitis media from Strep Pneumoniae?
antibiotics and myringotomy (drains pus from the middle ear by making small incision) with tympanostomy tubes
What is characteristicall seen in S. Pneumonaie culture?
autolysis of colonies - as organism die, the colonies fall apart leaving characteristic dimple (donut shaped)
What strep pneumo treatment is used on children?
penicillin or fluoroquinolone
What does enterococcus look like when cultured?
cocci in chains or lighter color diplococci
What test can be used to differentiate enterococcus from other bacteria?
bile esculin agar test (positive = dark color)
What are some characteristics of enterococcus that show its tough? (not from sketchy)
- can grow in pH 4-10
- refractory in metal salts
- live in temp rage from 5-50oC and survive 30min at 60oC
Where can enterococcus be naturally found?
part of normal flora-> lives in GI tract
What is the treatment of choice for E. faecalis?
ampicillin-sulbactam and aminoglycosides (gentamicin or streptomycin) synergistic therapy
*sulbactam = inhibitor of beta-lactamase allowing ampicillin to be effective
What is E. faecium resistant to?
vancomycin, ampicillin, and gentamicin (aminoglycoside)
What is the treatment of choice for E. faecium?
nitrofurantoin or linezolid or synercid
What are the different Strep Viridans?
S. Mutans, S. Sanguinis (cavities and endocarditis), S. milleri (endocarditis)
*all are part of normal flora
What’s the treatment of choice for mild infection of Strep (like impetigo)?
penicillin or tetracycline (if penicillin allergy)
