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Chapter 4: Streptococci


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How can you differentiate streptococci from staphylococci?
Catalase test: staph is positive
What do alpha, beta, and gamma hemolytic refer to?
Groups of streptococci, based on their ability to hemolyze RBCs
alpha = partial
beta = complete
gamma = none
Group A beta hemolytic strep:
- aka?
- Cause which diseases?
- Strep pyogenes
- Strep throat, scarlet fever, rheumatic fever, post-streptococcal glomerulonephritis, streptococcal skin infections, streptococcal toxic shock syndrome
How would you treat skin infections such as folliculitis, cellulites, and impetigo? Why?
Penicillinase resistant penicillin like dicloxacillin, because it covers both group A beta-hemolytic streptococci and Staph aureus, both of which can cause these skin infections
What is scarlet fever and how is it caused?
Certain beta-hemolytic group A streptococci produce pyrogenic/erythrogenic toxin, causing fever and a scarlet-red rash (sparing the face)
What is rheumatic fever?
Now rare, follows untreated beta-hemolytic group A streptococcal pharyngitis. Antibody mediated; manifests with fever, myocarditis, arthritis, chorea, subQ nodules, and an erythema marginatum rash. (Think of the John Travolta “Rheumatic Fever” picture).
What is acute post-strep glomerulonephritis?
Antibody-mediated disease occurring about one week after infection of either the pharynx or skin by nephritogenic strains of beta-hemolytic Group A strep
What are the Group B beta-hemolytic streptococci?
Think Group B “Baby.” Neonates can acquire these bugs during delivery, which can cause meningitis, pneumonia, and sepsis.
What are the three most common pathogens associated with meningitis in infants < 3 months?
E choli, Listeria, and Group B strep
What are the Viridans Group streptococci? What infections do they cause?
Heterogenous group of mostly alpha hemolytic streptococci. Normal GI flora. Think of ‘verde.’ Flora can bind to teeth… dental procedures can send these organisms into the blood stream. Cause: dental infections (cavities), subacute bacterial endocarditis, and abscesses
What could cause subacute bacterial endocarditis? Acute infective endocarditis? What are the clinical manifestations of each?
Viridans streptococci – low-grade fevers, fatigue, anemia, and heart murmur secondary to valve destruction.
Staphylococcal infection – abrupt onset of shaking chills, high spiking fevers, and rapid valve destruction.
What are enterococci? Are now resistant to⬦?
Gram positive alpha/gamma hemolytic streptococci. Normal bowel flora.
Resistant to ampicillin and vancomycin
Strep bovis infection has been shown to be associated with⬦?
Colon cancer
What is strep pneumo? Shape, virulence factor, lab tests?
Most common cause of adult pneumonia and bacterial meningitis. Most common cause of otitis media in children. Diplococci. Polysaccharide capsule. Quellung reaction and optochin sensitivity.
Which drugs are useful against strep pneumo with intermediate level resitance?
High dose penicillin and cephalosporins.

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