Flashcards in Streptococci Deck (47):
What discoloration do beta hemolytic streptococci leave after hemolysis of RBCs?
A clear zone of hemolysis around the halo.
What discoloration do alpha hemolytic streptococci leave?
They partially lyse the RBCS, leaving a greenish discoloration of the culture medium surrounding the colony.
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?
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?
What diseases does S.pyogenes cause?
1. Strep throat
2. Scarlet fever
3. Rheumatic fever
4. Post streptococcal glomerulonephritis
What components of the streptococcal cell wall are antigenic?
1. 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?
1. Streptolysin O (Oxygen labile - inactivated by oxygen)
2. Streptolysis S
3. Pyrogenic exotoxin (found in a few strains that cause scarlet fever)
5. Hyaluronidase, DNAases, anti-C5a peptidase
What are the 4 types of diseases that streptococci cause by local invasion and/or exotoxin release?
1. Streptococcal pharyngitis
2. Streptococcal skin infections
3. Scarlet fever
4. Streptococcal toxic shock syndrome
What are the two delayed antibody mediated diseases that beta hemolytic group A streptococci cause?
1. Rheumatic fever
2. Post streptococcal glomerulonephritis
What skin infections can streptococci cause?
These can also be caused by S.aureus.
Even with antibiotics and surgery, what is the mortality rate of necrotizing fasciitis?
Besides streptococci, what other pathogens can cause necrotizing fasciitis?
3. Gram- enterics
4. 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?
What percentage of women carry S.agalactiae vaginally?
What are the 3 MC organisms associated with meningitis in infants younger than 3 months?
1. Group B streptococci (S.agalactiae)
What 2 bacteria cause meningitis later in lifer?
What hemolysis do most Viridans group streptococci cause?
Greenish discoloration on blood agar, so they are alpha hemolytic.
What are the 3 types of infections that Viridans streptococci cause?
1. Dental infections
What is the Viridans streptococcus that causes dental infections?
What does the Anginosus species group contain?
Microaerophilic and part of normal GI tract.
What do you think if you find S.intermedius in the blood?
Streptococcus InterMeDius and AnginoSus
IMeDiately ASsess for ABSCESS.
What is another name for group D streptococci?
Enterococci and non-enterococci.
What hemolysis do group D streptococci produce?
Partial or no hemolysis. So, alpha or gamma hemolytic.
What are the enterococci?
E.faecalis and E.faecium.
What are the 2 most important non enterococci?
S.bovis and S.equinus.
What is unique about the growth of enterococci?
They all grow well in 40% bile or 6.5%NaCl.
What is the mechanism for VRE?
They have an acquired transposon called vanA that encodes a series of proteins that modify the D-alanine-D-alanine terminus of the peptidoglycan cell wall, changing it to D-alanine-D-lactate, which has low affinity for vancomycin.
What is even more scary about VRE?
They can transfer vanA gene to the really nasty S.aureus.
How do we differentiate S.bovis from the enterococci?
S.bovis grows well in 40% bile, but not in 6.5% NaCl.
What is important to keep in mind about S.bovis?
Association with colon cancer.
Does S.pneumoniae have a Lancefield antigen?
Why is S.pneumoniae important?
1. Major cause of bacterial pneumonia and meningitis in adults.
2. Otitis media in children.
What is the major virulence factor of S.pneumoniae?
Its polysaccharide capsule, which protects the organism from phagocytosis.
Is the capsule of S.pneumoniae antigenic?
How many different capsule serotypes exist?
What are the 2 important tests for identifying pneumococcus?
1. Quellung reaction
2. Optochin sensitivity
What is the importance of optochin sensitivity?
S.pneumoniae is alpha hemolytic, but S.viridans is also alpha hemolytic.
Optochin inhibits the growth of S.pneumoniae, while S.viridans will continue to grow.