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is brought to his primary care physician
with vesicular lesions over his face, some of which
have ruptured. He has no history of fever or other
symptoms. Physical examination reveals several vesicles.
Golden, beta-hemolytic colonies are grown on
blood agar culture of the exudate.Which of the following
features would most likely be associated with the
probable pathogen?
(A) Alpha hemolysis
(B) Bacitracin sensitivity
© Catalase negativity
(D) Coagulase positivity
(E) Streptokinase positivity
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cccccccccc...streptococcal impetigo
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streptokisase +VE>....... how is that one......
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The correct answer is D. Impetigo is a superficial vesiculopustular
skin infection occurring prominently on
exposed areas of the face and extremities. It is typically
caused by Staphylococcus aureus or Streptococcus pyogenes.
In this case, the golden beta-hemolytic colonies are
most likely S. aureus. Unlike S. pyogenes, S. aureus often
produces a golden pigment and is coagulase-positive.
Alpha hemolysis (choice A) leaves the RBCs in an agar
plate intact, but the hemoglobin is converted to
biliverdin. This causes a greening of the plate.
Hemolysis is important in classifying the streptococci.
Alpha hemolysis is characteristic of both Streptococcus
pneumoniae and the viridans streptococci.
Bacitracin sensitivity (choice B) is used to distinguish S.
pyogenes, or group A streptococcus, from other betahemolytic
streptococci. S. pyogenes is sensitive to the
antibiotic bacitracin. All other beta-hemolytic streptococci
are resistant to the antibiotic.
Catalase negativity (choice C) distinguishes the genus
Streptococcus from the genus Staphylococcus. Streptococci
lack the enzyme catalase, which catalyzes the conversion
of hydrogen peroxide to water and oxygen gas.
Streptokinase positivity (choice E) is a property of S. pyogenes.
Streptokinase hydrolyzes fibrin and other host proteins
helping the organism spread through tissues. The
purified enzyme is used clinically to dissolve blood clots.
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so ans is staph!!...how come he is apyrexial.....absent of fever is characteristic of stpt not staph....but i guess the clue was golden beta hemolytic coloney
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u right darkhorse, i found intersting that just one word is a clue to answer the qs: the golden beta-hemolytic colonies are most likely S. aureus.
Good point
