Lecture 4 - Gram Positive Cocci (STREP) Flashcards
Streptococci
- Arranged in pairs or chains
- Grows on blood agar
Streptococci:
Groups
- haemolytic properties (alpha, beta)
- carboydrate C antigen (Lancefield classification)
- M-protein
- —> divides beta-haemolytic
- —>mostly group A
Haemolytic Phaemolytic Properties:
Alpha
- Greenish brown
- Partially destroys RBC
Haemolytic Phaemolytic Properties:
Beta
- Destroys completely the RBC
- Clear zone around colonies
Carbohydrate C Antigen
- Extracted from the cell wall, subdivides streptococci in groups A-T (lancer field)
M-Protien
- Permits subdivision of beta-haemolytic streptococci into over 70 serotypes
- Mostly in group A
Haemolytic Phaemolytic Properties:
Gamma
Not hemolytic
Group A, beta-hemolytic, Streptococcus pyogenes causes:
- acute tonsillitis (strept throat) – can lead to rheumatic heart disease
- impetigo, cellulitis, etc. (skin infections)
- fever and septicaemia
Streptococcus pyogenes:
Caused by toxins
- streptolysins (O and S)
• neutrophils and macrophages - streptococcal pyrogenic exotoxins (Spes)
• scarlet fever rash
Streptococcus pyogenes:
Enzymes
- Hyaluronidase (helps spreading of bacteria)
- Virtually all are penicillin G sensitive
- Transmission by direct contact (nasal is more easily transmitted)
- Contaminated food can cause outbreaks
Streptococcus pyogenes:
Prevention
- Education of health personnel
- Aseptic obstetric procedures (puerperal fever)
- Early detection and treatment
Necrotizing Fasciitis
- Streptococcus pyogenes culprit
- Does not actually “eat” anything
- Toxin is responsible for damage
Necrotizing Fasciitis:
How does it happen? Theories
- hijacking human plasminogen from blood, attach to surface and
activate it into protease…good for spreading… - bacteriophage has gene encoding for enzyme allowing bacteria to escape entrapment and killing by neutrophils (white blood cells)
Group B: Streptococcus agalactiae
- Found in vagina of health women (can cause neonatal infections)
Group B: Streptococcus agalactiae
Early Septicaemia
- respiratory distress or shock at birth
- high fatality rate (serious)
Group B: Streptococcus agalactiae
Delayed Meningitic Form
- 1-12 weeks post-partum
- sequelae
Streptococcus pneumoniae
- Also known as pneumococcus
- Polysaccharide capsule has antiphagocytic properties
- ~90 distinct capsular serotypes
Streptococcus pneumoniae:
Found where?
Found in naso-pharynx of healthy individuals
Streptococcus pneumoniae:
Causes
- lobar pneumonia
- meningitis
Streptococcus pneumoniae:
Prevention
- elderly
- alcoholics
- crowded living
- vaccination
