Streptococci Flashcards
How are the different species distinguished?
Examining haemolysis of blood afar
Large zone of complete haemolysis is called?
Beta haemolysis
Colonies surrounded by green/brown zones on blood agar is called?
Alpha haemolysis
What is Lancefield Grouping?
A latex agglutination test to determine immunological groups. Beads are coated in antibodies and will clump together if the appropriate antigen is present
Where is S.pyogenes commonly found
Upper respiratory tract
What diseases can s.pyogenes cause
Streptococcal pharyngitis (strep throat) Otitis media & mastitis Scarlet Fever Necrotising fascilitis Rheumatic fever Acute glomerulonephritis
Symptoms of streptococcal pharyngitis
Severe sore throat, enlarged tonsils, tonsillar exudates, tender cervical lymph nodes, mild fever
What is Scarlet Fever
Caused by strains carrying a lysogenic bacteriophage (virus) coding for an exotoxin.
Pink/red rash caused by damage to small blood vessels, and a fever
What causes necrotising fascilitis
Exotoxins A&B recruit T cells to infected tissues, which secrete cytokines activating effector cells and leading to massive inflammation, tissue destruction, and death in 30% of cases
How is rheumatic fever caused
Some of the antigens on the bacteria are similar to human cell-surface antigens.
Heart, joints, kidneys mostly affected
How is acute glomerulonephritis caused?
Streptococcal antigen-antibody complexes we lodged in the glomeruli of kidneys, causing pain that lasts a few days
What is Streptococcus pneumoniae
A lung infection causing fluid and cells to accumulate in the lungs. Bacteria invade alveolar tissue of lower respiratory tract, causing a strong inflammatory response.
S.pneumoniae has a capsule allowing it to survive phagocytosis
