ORGANISMS - STREPS Flashcards
(34 cards)
What gram is a streptococcus?
GRAM POSITIVE
How are they arranged?
ARRANGED IN CHAINS, STAPHS IN CLUMPS
Are they catalase +ve or -ve?
NEGATIVE
Are they anaerobic or aerobic?
ANAEROBIC
Give the names of the 3 types of classification and describe the breakdown of blood agar for each type
ALPHA HAEMOLYSIS - viridans group, partial breakdown (green)
BETA HAEMOLYSIS - most common, complete breakdown
GAMMA HAEMOLYSIS - enterococci, no break down, no clear space.
Why cant haemolysis occur on chocolate agar?
Haemolysis is break down of blood, and in chocolate agar this has already occured. results would always look green.
Give examples of a typical case patient for Strep. pneumoniae infection
Elderly, cough, chest pains, purulent sputum, chill and developed fever, high temp
How to diagnose Strep. pneumoniae
- Easy to spot in sputum smear
- Quelling reaction - anticapsular antibodies cause capsule to swell, easily visible.
- Dimpled colonies.
- Optochin sensitive - only strep is sensitive to this
What are the most medically important Lancefield groups?
A,B and D
Why cant Strep. Pneumoniae and Strep. viridans be identified in Lancefield grouping?
This method is only for beta haemolytic streps and they are both alpha haemolytic
Give 2 examples of non-invasive Strep. pyogenes infections
ANY FROM pharyngitis (strep throat), impetigo, scarlet fever, cellulitis
Give 2 examples of invasive Strep. pyogenes infections
ANY FROM toxic shock type syndrome, necrotising fasciiitis, rheumatic fever, glomerulonephritis
Give symptoms of strep throat (pharyngitis)
Hot, flushed, sore throat, vommiting, high temp, red throat, greyish white exudate, enlarged lymph nodes
Complications and Symptoms of scarlet fever
- Rash
- Strawberry tongue
- If organism produces SPE (erythrogenic) toxin = scarlet fever
- Rash dissapears 1 week later then skin sloughs.
Complications and Symptoms of rheumatic fever
- Life threatening: joints, fever, heart
- Damage to rheumatic joints
- Damage to heart valves (scarring)
- Autoimmune response - anti strep antibodies react with heart antigens
Give examples of complications of acute rheumatic fever
- Fatalities - heart failure
- Scaring of valves
- Prevention - penicillin treatment of pharyngitits
- Number of cross reactive agents (auto immune disease)
What is the mode of action of Strep. pyogenes?
- ATTACHMENT
- MULTIPLICATION
- SPREAD (all by adhesions, important in throat, pharynx infections)
- ADHESIONS such as lipotechioic acid (LTA) M proteins
Explain the multiplication stage of Strep. pyogenes infection.
- M-protein, bind fibrinogen, fibrin and degradation products.
- blocks complement attachment
- binds factor H - inhibits complement cascade.
- resistant to phagocytosis
- nearly 100 diff m-types
Name the 3 ways Strep. pyogenes spreads
SKIN - localised
PHARYNX - far as ears or sinuses
WOUND - rapid spread, aided by virulence proteins
Name 3 of Strep. pyogenes virulence factors
proteases, Dnase, streptokinase, hyaluronidase
What are the actions of streptokinase?
- Induces fibrinolysis. (degrades fibrin and other proteins, affects clotting).
- This helps to spread as clotting localises infection
What are the actions of hyaluronidase?
- breaks down hyaluronic acid in connective tissue.
- bactiera shut off capsule production
- turn on hyaluronidase production at epithelial surface.
Name 3 ways in which Strep. pyogenes causes damage
ANY 3 FROM - pyrogenic toxins, ABC, erythrogenic toxins, suppress antibody responses, stimulate cytokines (SEPTIC SHOCK) streptolysins.
How would Strep. pyogenes be diagnosed in a lab situation?
- culture of pus and blood
- bacitracin sensitive
