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Old 07-18-2011
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Bacteria The type colony that will be formed by this bug!

A patient on hemodialysis develops low-grade fevers. Blood cultures drawn from the dialysis access catheter grow gram-positive cocci that are catalase positive and coagulase negative. What colonies will this organism form?
A. Alpha-hemolytic white colonies
B. Nonhemolytic white colonies
C. Alpha-hemolytic yellow colonies
D. Nonhemolytic yellow colonies
E. Beta-hemolytic yellow colonies
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Default Staph Epidermidis - Non hemolytic white colonies!

  • Gram Positive Cocci -either staph or strep
  • Catalase positive - differentiates to staph (strep is catalase -)
  • Coagulase Negative - staph epidermidis or staph saprophyticus
  • Infection from catheter - points to S. Epidermidis

S. Epidermidis is non-hemolytic, so this eliminates choices A,C,E & leaves us with B & D.

S.Epidermidis forms non-hemolytic WHITE colonies.

The answer is B. Non-hemolytic white colonies.
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B. Nonhemolytic white colonies (yup, gamma hemolysis)

The type colony that will be formed by this bug!-hemolisis.jpg
click image to enlarge
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Old 07-19-2011
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Default

The correct answer is B.
S. epidermidis forms nonhemolytic, white colonies (originally named Staphylococcus albus; "albus" means white). While staphylococcal species can cause hemolysis of blood agar, the classification of alpha-hemolysis vs. beta-hemolysis is most commonly applied to streptococcal classification. S. aureus forms hemolytic yellow colonies ("aureus" means gold/yellow
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