Gram Positive Cocci: Staphylococci and Streptococci (pics) Flashcards
Staphylococcus aureus
aureus on Blood Agar Plate
Clumping Factor Positive and Negative
Coagulase test
LEFT:(+), indicating the presence of coagulase (converts fibrinogen→fibrin, resulting to clotting).
Catalase test
LEFT: (+). Catalase converts H2O2→ O2 + H2O, as evidenced by bubbles.
Mannitol Salt Agar Plate
LEFT: S. Aureus (+), with fermentation of Mannitol. RIGHT: (-)
Morphology of Genus Streptococcus
Patterns of hemolysis
ellow: B-hemolysis, Green: α-Hemolysis, White: non-hemolytic
Bacitracin Test
Agar plate on the right containing S. pyogenes shows sensitivity to Bacitracin (clear zone of inhibition)
Antigen detection test for S. pyogenes
LEFT: positive clumping.
Streptococcus pneumonia in sputum
Seen as lancet-shaped gram-positive diplococci. Degenerating nuclei of PMN cells are the large darker irregular red shapes (black arrow).
Optochin Test
(a) Optochin inhibition and bile solubility of S. pneumoniae - note the presence of the zone of inhibition. (b) The growth of viridans streptococci is not inhibited by optochin.
Broth culture method
A positive test for the broth culture method is observed in the clearance in the test set-up (right) as opposed to the control set-up (left).
S. pneumonia quellung reaction
positive reaction shows clumping because of cross-linking of the antibodies and pneumococci. The halo effect is apparent capsular swelling. A negative control would show no clumping or capsular swelling.
