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Microbiology > Streptococci > Flashcards

Streptococci Flashcards

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Biology 101 flashcards
0
Q

What discoloration do alpha hemolytic streptococci leave?

A

They partially lyse the RBCS, leaving a greenish discoloration of the culture medium surrounding the colony.

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1
Q

What discoloration do beta hemolytic streptococci leave after hemolysis of RBCs?

A

A clear zone of hemolysis around the halo.

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2
Q

What does the discolored area of alpha hemolytic streptococci contain?

A

A green-colored metabolite of Hb.

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3
Q

Can gamma hemolytic streptococci lyse the RBCs?

A

No, so they are often termed non-hemolytic streptococci.

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4
Q

What are the Lancefield antigens?

A

The different antigenic characteristics of the C carbohydrate - found in the cell wall of streptococci. (A, B, C, through S).

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5
Q

Although there are more than 30 species of streptococci, how many are significant human pathogens?

A

Only 5.

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6
Q

The 3 of the 5 streptococcal species that are human pathogens have what Lancefield antigens?

A

A,B,D. The other 2 do not have Lancefield antigens.

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7
Q

What are the two streptococci that do not have Lancefield antigens?

A

S.pneumoniae and Viridans group streptococci.

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8
Q

How are group A beta hemolytic streptococci also called?

A

S.pyogenes

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9
Q

What diseases does S.pyogenes cause?

A
  1. Strep throat
  2. Scarlet fever
  3. Rheumatic fever
  4. Post streptococcal glomerulonephritis
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10
Q

What components of the streptococcal cell wall are antigenic?

A
  1. C carbohydrate (Lancefield Group A)

2. M protein (80 different types)

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11
Q

What is the action of the M streptococcal protein?

A

This is a major virulence factor for the group A streptococcus.
It inhibits the activation of complement and protects the organism from phagocytosis.

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12
Q

What pathogenic enzyme do beta hemolytic group A streptococci possess?

A
  1. Streptolysin O (Oxygen labile - inactivated by oxygen)
  2. Streptolysis S
  3. Pyrogenic exotoxin (found in a few strains that cause scarlet fever)
  4. Streptokinase
  5. Hyaluronidase, DNAases, anti-C5a peptidase
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13
Q

What are the 4 types of diseases that streptococci cause by local invasion and/or exotoxin release?

A
  1. Streptococcal pharyngitis
  2. Streptococcal skin infections
  3. Scarlet fever
  4. Streptococcal toxic shock syndrome
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14
Q

What are the two delayed antibody mediated diseases that beta hemolytic group A streptococci cause?

A
  1. Rheumatic fever

2. Post streptococcal glomerulonephritis

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15
Q

What skin infections can streptococci cause?

A
  1. Folliculitis
  2. Pyoderma
  3. Erysipelas
  4. Cellulitis
  5. Impetigo
    These can also be caused by S.aureus.
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16
Q

Even with antibiotics and surgery, what is the mortality rate of necrotizing fasciitis?

A

> 50%.

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17
Q

Besides streptococci, what other pathogens can cause necrotizing fasciitis?

A
  1. Staphylococcus
  2. Clostridium
  3. Gram- enterics
  4. Mixed infection of the above
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18
Q

What is the Fournier’s gangrene?

A

A forma of necrotizing fasciitis involving the male genital area and perineum.
Often caused by mixed organisms but can be caused by S.pyogenes.

19
Q

How is Scarlet fever caused?

A

From an exotoxin - pyrogenic or erythrogenic toxin.

20
Q

How do we treat severe S.pyogenes infections, such as severe skin infections, necrotizing fasciitis, and streptococcal toxic shock syndrome?

A

With high dose penicillin and with clindamycin.

21
Q

What is another name for group B beta-hemolytic streptococci?

A

S.agalactiae

22
Q

What percentage of women carry S.agalactiae vaginally?

A

About 25%

23
Q

What are the 3 MC organisms associated with meningitis in infants younger than 3 months?

A
  1. Group B streptococci (S.agalactiae)
  2. E.coli
  3. L.monocytogenes
24
Q

What 2 bacteria cause meningitis later in lifer?

A
  1. N.meningitidis

2. H.influenza

25
Q

What hemolysis do most Viridans group streptococci cause?

A

Greenish discoloration on blood agar, so they are alpha hemolytic.

26
Q

What are the 3 types of infections that Viridans streptococci cause?

A
  1. Dental infections
  2. Endocarditis
  3. Abscesses
27
Q

What is the Viridans streptococcus that causes dental infections?

A

S.mutans

28
Q

What does the Anginosus species group contain?

A
  1. S.intermedius
  2. S.constellatus
  3. S.anginosus
    Microaerophilic and part of normal GI tract.
29
Q

What do you think if you find S.intermedius in the blood?

A

Streptococcus InterMeDius and AnginoSus

IMeDiately ASsess for ABSCESS.

30
Q

What is another name for group D streptococci?

A

Enterococci and non-enterococci.

31
Q

What hemolysis do group D streptococci produce?

A

Partial or no hemolysis. So, alpha or gamma hemolytic.

32
Q

What are the enterococci?

A

E.faecalis and E.faecium.

33
Q

What are the 2 most important non enterococci?

A

S.bovis and S.equinus.

34
Q

What is unique about the growth of enterococci?

A

They all grow well in 40% bile or 6.5%NaCl.

35
Q

What is the mechanism for VRE?

A

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.

36
Q

What is even more scary about VRE?

A

They can transfer vanA gene to the really nasty S.aureus.

37
Q

How do we differentiate S.bovis from the enterococci?

A

S.bovis grows well in 40% bile, but not in 6.5% NaCl.

38
Q

What is important to keep in mind about S.bovis?

A

Association with colon cancer.

39
Q

Does S.pneumoniae have a Lancefield antigen?

A

No.

40
Q

Why is S.pneumoniae important?

A
  1. Major cause of bacterial pneumonia and meningitis in adults.
  2. Otitis media in children.
41
Q

What is the major virulence factor of S.pneumoniae?

A

Its polysaccharide capsule, which protects the organism from phagocytosis.

42
Q

Is the capsule of S.pneumoniae antigenic?

A

Yes.

43
Q

How many different capsule serotypes exist?

A

84

44
Q

What are the 2 important tests for identifying pneumococcus?

A
  1. Quellung reaction

2. Optochin sensitivity

45
Q

What is the importance of optochin sensitivity?

A

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.

46
Q

What S.pneumoniae serotypes are the MCC of otitis media?

A 
3
6B
9V
14
19F
23F

Microbiology (46 decks)

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