Streptococci Flashcards
key characteristics of Streptococci
◾ 1 µm in diameter
◾ chains or pairs
◾ usually capsulated
◾ non-motile
◾ non-spore forming
◾ facultative anaerobes
◾ fastidious
◾ catalase negative
◾ [Image]
Streptococcus pyogenes haemolysis
β
briefly comment on capsule of S. pyogenes
it is made of hyaluronic acid
List three superficial infections of S. pyogenes.
Name three toxin-mediated symptoms of S. pyogenes infection.
◾ Scarlet fever
◾ Toxic shock-like syndrome
◾ Necrotising fasciitis
Name three immunologically mediated complications of S. pyogenes infection.
◾ rheumatic fever
◾ post-streptococcal glomerulonephritis
◾ reactive arthritis
list virulence factors of S. pyogenes
(1) M protein
(2) Hyaluronic acid capsule
(3) Lipoteichoic acid
(4) Protein F (fibronectin-binding protein)
(5) Exotoxins: Streptolysin O, Streptolysin S, Streptococcal pyrogenic exotoxins (SpeA, SpeB, SpeC)
(6) Enzymes: streptokinase, hyaluronidase, streptodornase (DNase), C5a peptidase
State two effects of S. pyogenes M protein.
(1) Immune evasion; anti-phagocytic and interferes with the complement system
(2) Autoimmune responses; it may trigger autoimmune responsess such as acute rheumatic fever due to molecular mimicry [tropomyosin]
Which of Strep. pyogenes exotoxins are superantigens?
(1) Streptococcal Pyrogenic Exotoxin A (SpeA)
(2) Streptococcal Pyrogenic Exotoxin C (SpeC)
Which of Strep. pyogenes exotoxins causes necrotizing fasciitis?
(1) Streptococcal Pyrogenic Exotoxin A (SPE A)
What type of S. pyogenes infection precipitates rheumatic fever?
pharyngitis
What type of S. pyogenes infection precipitates post-streptococcal glomerulonephritis?
(1) Pharyngitis
(2) Skin infections [impetigo]
Name 5 virulence factors of S. pyogenes.
(1) Capsule
(2) Streptolysin O
(3) Streptokinase
(4) DNAse
(5) SpeA-C
One key distinguishing feature between GAS and GBS?
GAS is Bacitracin sensitive.
Which member of the Streptococcus genus has a positive hippurate test?
S. agalactiae
Does S. agalactiae have a capsule?
Yes
What test distinguishes S. agalactiae from all other Strep. species?
positive CAMP test
virulence factors of GBS
(1) Extracellular enzymes: CAMP factor, cytolysin, hyaluronidase, C5a peptidase
(2) Capsular polysaccharide
(3) Adhesins
GBS clinical manifestations in newborns
(1) Early onset disease: occurs within the first week of life; sepsis, meningitis, pneumonia
(2) Late-onset disease: occurs after the first week of life; meningitis, bacteremia
How do neonates get infected with Strep. agalactiae?
Infected during passage through birth canal
GBS clinical manifestations in pregnant women
◾ urinary tract infections
◾ chorioamnionitis
◾ endometritis
GBS clinical manifestations in non-pregnant adults
bacteremia, pneumonia, skin and soft tissue infections, bone and joint infections, meningitis
Hemolysis: Strep. agalactiae
β
GBS identification tests
catalase negative, Bacitracin resistance, positive CAMP test, penicillin sensitive
