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Sporothrix schenckii
4%
20/468
Streptococcus mitis
1%
6/468
Streptococcus mutans
5/468
Staphylococcus epidermidis
5%
25/468
Streptococcus pyogenes
88%
410/468
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The presentation of the pustular rash along with the culture showing catalase-negative, beta-hemolytic Gram-positive cocci in chains points to Streptococcus pyogenes (also known as group A strep) as the causative agent for the rash. S. pyogenes is the only one of the above infectious agents that is beta-hemolytic. S. pyogenes is sensitive to bacitracin. The virulence factors that aid in S. pyogenes' spread and inflammation are the following: hyaluronidase aids in the break down of connective tissue, streptokinase converts plasminogen to plasmin promoting fibrinolysis, DNase digests cellular DNA, and the M protein prevents the host's immune system from phagocytosing the bacteria. Figure A shows an example of impetigo; yellow crusts have formed along the border of the rash. Incorrect Answers: Answer 1: Sporothrix schenckii is a fungus that is normally found in soil or plants such as roses (Rose Gardener's Disease). When cultured at different temperature it either presents as branched hyphae at 25 degrees Celsius or as single cells at 37 degrees Celsius Answer 2-3: Streptococcus mutans and mitis are alpha-hemolytic, bile-esculin negative, optochin-resistant Gram + cocci. Answer 4: Staphylococcus epidermidis is a catalase +, coagulase -, novobiocin-sensitive Gram + cocci.
3.5
(17)
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