Streptococci Flashcards
What discoloration do alpha hemolytic streptococci leave?
They partially lyse the RBCS, leaving a greenish discoloration of the culture medium surrounding the colony.
What discoloration do beta hemolytic streptococci leave after hemolysis of RBCs?
A clear zone of hemolysis around the halo.
What does the discolored area of alpha hemolytic streptococci contain?
A green-colored metabolite of Hb.
Can gamma hemolytic streptococci lyse the RBCs?
No, so they are often termed non-hemolytic streptococci.
What are the Lancefield antigens?
The different antigenic characteristics of the C carbohydrate - found in the cell wall of streptococci. (A, B, C, through S).
Although there are more than 30 species of streptococci, how many are significant human pathogens?
Only 5.
The 3 of the 5 streptococcal species that are human pathogens have what Lancefield antigens?
A,B,D. The other 2 do not have Lancefield antigens.
What are the two streptococci that do not have Lancefield antigens?
S.pneumoniae and Viridans group streptococci.
How are group A beta hemolytic streptococci also called?
S.pyogenes
What diseases does S.pyogenes cause?
- Strep throat
- Scarlet fever
- Rheumatic fever
- Post streptococcal glomerulonephritis
What components of the streptococcal cell wall are antigenic?
- C carbohydrate (Lancefield Group A)
2. M protein (80 different types)
What is the action of the M streptococcal protein?
This is a major virulence factor for the group A streptococcus.
It inhibits the activation of complement and protects the organism from phagocytosis.
What pathogenic enzyme do beta hemolytic group A streptococci possess?
- Streptolysin O (Oxygen labile - inactivated by oxygen)
- Streptolysis S
- Pyrogenic exotoxin (found in a few strains that cause scarlet fever)
- Streptokinase
- Hyaluronidase, DNAases, anti-C5a peptidase
What are the 4 types of diseases that streptococci cause by local invasion and/or exotoxin release?
- Streptococcal pharyngitis
- Streptococcal skin infections
- Scarlet fever
- Streptococcal toxic shock syndrome
What are the two delayed antibody mediated diseases that beta hemolytic group A streptococci cause?
- Rheumatic fever
2. Post streptococcal glomerulonephritis
What skin infections can streptococci cause?
- Folliculitis
- Pyoderma
- Erysipelas
- Cellulitis
- Impetigo
These can also be caused by S.aureus.
Even with antibiotics and surgery, what is the mortality rate of necrotizing fasciitis?
> 50%.
Besides streptococci, what other pathogens can cause necrotizing fasciitis?
- Staphylococcus
- Clostridium
- Gram- enterics
- Mixed infection of the above
What is the Fournier’s gangrene?
A forma of necrotizing fasciitis involving the male genital area and perineum.
Often caused by mixed organisms but can be caused by S.pyogenes.
How is Scarlet fever caused?
From an exotoxin - pyrogenic or erythrogenic toxin.
How do we treat severe S.pyogenes infections, such as severe skin infections, necrotizing fasciitis, and streptococcal toxic shock syndrome?
With high dose penicillin and with clindamycin.
What is another name for group B beta-hemolytic streptococci?
S.agalactiae
What percentage of women carry S.agalactiae vaginally?
About 25%
What are the 3 MC organisms associated with meningitis in infants younger than 3 months?
- Group B streptococci (S.agalactiae)
- E.coli
- L.monocytogenes
