Chapter 2: Streptococci Flashcards
Streptococci is:
gram-positive non-motile catalase negative aerotolerant anaerobes (grow fermentatively even in the presence of oxygen) culture on blood enriched medium
All the followings are true exept:
a. α-Hemolytic streptococci cause complete hemolysis of red cells in blood agar, resulting in the appearance of a red pigment that forms a ring around the colony
b. β-Hemolytic streptococci cause gross complete hemolysis of red blood cells, resulting in a clear ring around the colony.
c. γ-Hemolytic no color change or hemolysis in blood agar
a:
α-Hemolytic streptococci cause partial hemolysis of red cells in blood agar, resulting in the appearance of a green pigment that forms a ring around the colony
1st step in the classification of streptococci:
Hemolysis pattern
True or False:
Many species of staphylococci have a polysaccharide in their cell walls known as C-antigen, which is antigenic and easily extractable with dilute base or Boiling.
False:
Many species of streptococci have a polysaccharide in their cell walls known as C-antigen, which is antigenic and easily extractable with dilute acid or Boiling.
The Lancefield scheme classifies primarily ……….. into groups A to H and K to U on the basis of their ……
β-hemolytic streptococci, C-antigen
there are 20 C-antigen
Match the following β-hemolytic streptococci with their names:
β-hemolytic streptococci A strep.bovis
β-hemolytic streptococci B strep. agalactiae
β-hemolytic streptococci D strep. pyogenes
β-hemolytic streptococci A => strep. pyogenes
β-hemolytic streptococci B => strep. agalactiae
β-hemolytic streptococci D => strep.bovis
Some strains of S. pyogenes cause postinfectious sequelae, including:
- rheumatic fever and
- acute glomerulonephritis.
Structural features involved in the pathology or identification of group A streptococci include:
- Capsule: Hyaluronic acid identical to human, non-immunogenic, anti-phagocytic
- Cell wall
- Extracellular products: exotoxins
Which of the following is not a component of S.pyogens cell wall: M protein Hyaluronic acid Group A-specific C-antigen: Protein F (fibronectin-binding protein)
Hyaluronic acid
M protein:
- S. Pyogenes is not infectious in the absence of M protein.
- highly variable, especially the N-terminal regions, resulting in over 80 different antigenic types.
- individuals may have many S. pyogenes infections throughout their lives as they encounter new M protein types
- anti-phagocytic and they form a coat that interferes with complement binding.
Group A-specific C-antigen is composed of:
- rhamnose and
- N-acetylglucosamine.
All of the followings mediate the attachment of fibronectin in the pharyngeal epithelium except:
a. Protein F
b. Group A-specific C-antigen
c. lipoteichoic acids
d. M proteins
b. Group A-specific C-antigen
True or False:
S.pyogenes may simply replicate sufficiently with causing injury in which case the patient is then considered colonized (carrier).
False:
it may simply replicate sufficiently without causing injury
True or False:
However, direct inoculation of skin from another person’s infection can lead to:
- streptococcal skin infection and
- soft tissue infection.
True
Syndromes caused by pyogenes:
- Acute pharyngitis or pharyngotonsilitis:
- Impetigo
- Erysipelas
- Puerperal sepsis:
- Invasive group A streptococcal disease: Cellulitis or
“flesh-eating bacteria - Streptococcal toxic shock syndrome:
- Post-streptococcal sequelae: a. Acute rheumatic fever. b. Acute glomerulonephritis
Which of the following statements is wrong:
a. S. Pyogenes is a major cause of cellulitis.
b. Pharyngitis is the most common type of S. pyogenes infection.
c. Many strep throats are severe, and many sore throats caused by viruses are mild.
c:
Many strep throats are mild, and many sore throats caused by viruses are severe.
Treatment of impetigo:
topically
systemically
- topical agent: mupirocin
- systemically with
- penicillin or a
- first-generation cephalosporin: cephalexin,
Puerperal sepsis:
- starts during, or soon after, the delivery of a newborn.
- caused by:
1) exogenous transmission (by nasal droplets from an infected carrier or from contaminated instruments) or
2) endogenously (mother’s vaginal flora) - a disease of the uterine endometrium in which patients experience a purulent vaginal discharge and are systemically ill.
Symptoms of invasive GAS disease:
fhm st
- toxic shock–like syndrome,
- fever,
- hypotension,
- multi-organ involvement,
- a sunburn like rash
- or a combination of these symptoms
Patients with streptococcal TSS may initially present with:
fn sar
flulike symptoms
followed shortly by necrotizing soft tissue infection, shock,
acute respiratory distress syndrome,
and renal failure.
Treatment of streptococcal TSS:
high-dose of: penicillin G plus clindamycin.
Acute rheumatic fever
- autoimmune disease
- 2 to 3 weeks after start of pharyngitis.
- caused by cross-reactions
- fever, rash, carditis, and arthritis, Sydenham’s chorea(uncontrolled movement, loss of fine motor control)
- preventable if the patient is treated within the first 10 days
Acute glomerulonephritis
- 1 week after impetigo or pharyngitis
- due to a few nephritogenic strains of grp 1 strep
- Antigen-antibody complexes on the basement membrane of the glomerulus initiate the disease.
- no evidence that penicillin treatment can prevent it
True or False:
Rapid latex antigen kits tests have high specificity but variable sensitivity compared with culture techniques.
True
