9. Streptococci Flashcards
What class of bacteria is streptococci
Gram positive, chains
What is haemolysis?
Using the ability of bacteria to breakdown red blood cells as a way of classifying the different micro organisms
What colour does alpha haemolysis create? Give an example of a bacteria that carries out alpha haemolysis
Dark green
Viridans streptococci eg spretococcus pneumoniae
What is beta haemolysis? Give an example of a bacteria that displays beta haemolysis
Complete haemolysis - produces a lightened (yellow) transparent area
Streptococcus pyogenes
What is gamma haemolysis? Give an example of a bacteria that displays game haemolysis
No haemolysis occurs, so still looks the same.
Enterococcus faecalis
What are the two different classification schemes for streptococci bacteria?
Lancefield, based on cell wall antigens, is letters
Sherman, eg pyogenic, viridans etc
What main class of bacteria causes abscesses?
Pyogenic
Give 2 virulence factors of streptococcus pyogenes
Hyaluronic acid capsule - inhabiting phagocytosis by neutrophils and macrophages, and making it a poor immunogenicity due to similarity to human connective tissue hyaluronate
M protein - resistance to phagocytosis by inhibiting activation of alternative complement pathway on bacterial cell surface
Adhesions - aiding colonisation/infection
What is the bacterial cause of streptococcal pharyngitis?
Streptococcus pyogenes
How is streptococcal pharyngitis spread?
Droplet spread, associated with overcrowding
What do untreated patients with streptococcal pharyngitis develop?
M protein specific antibody (aid in opsonisation and destruction of the microorganism my macrophages and neutrophils)
Name 4 complications of streptococcal pharyngitis
Scarlet fever
Suppurative complications eg meningitis (brain abscess)
Acute rheumatic fever
Acute post-streptococcal glomerulonephritis
What is scarlet fever? What causes it?
Infection with streptococcal pyogenic exotoxin strain of S.pyogenes.
Local or haematogenous spread.
High fever, sepsis, arthritis, jaundice
What is acute rheumatic fever? Give 2 possible causes of it
Inflammation of the heart, joints, central nervous system. Occurs ONLY after pharyngitis, not from other streptococcal infections
There are rheumatogenic M types
Auto-immune, binding of M protein to collagen
What is acute post-streptococcal glomerulonephritis? What causes it?
Acute inflammation of the renal glomerulus
M type specific
Antigen-antibody complexes deposited in the glomerulus
What is impetigo? What secondary condition is it the most common cause of?
Common in children 2-5yrs
Skin colonisation and then intradermal inoculation
Most common cause of glomeruonephritis
What is erysipelas?
Dermis infection with lymphatic involvement, affecting the face and lower limbs
Facial lesions preceded by pharyngitis
Lower limb infection usually secondary to trauma, skin disease or local fungal infection leading to streptococcus pyogenes invasion of the skin
What is cellulitis? What are two important risk factors for developing cellulitis?
Skin and subcutaneous tissue infection
Impaired lymphatic drainage and illicit injecting drug use
What is necrotising fasciitis? What is it associated with?
Infection of deeper subcutaneous tissues and fascia, with rapid, extensive necrosis, usually secondary to skin break
Severe pain even before gross clinical changes
High fever, very rapid onset, high mortality
What is streptococcal toxic shock syndrome?
Deep tissue infection with strep pyogenes, bacteraemia, vascular collapse, organ failure (thought to be caused by formation of M-protein fibrinogen complex)
Give 3 infections that streptococcus pneumoniae can cause
Community-acquired pneumonia
Adult bacterial meningitis
Sinusitis
Is streptococcus pneumoniae gram positive or negative?
Gram-positive
What two properties does the capsule of streptococcus pneumoniae possess?
Antiphagocytic
Antigenic
Does pharyngitis caused by streptococcus pyogenes cause white exudate to form on the throat and tonsils?
Yes, EBV does not
