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The page below is a sample from the LabCE course Preliminary Identification of the Primary Select Agents of Bioterrorism. Access the complete course and earn ASCLS P.A.C.E.-approved continuing education credits by subscribing online.

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Y. pestis on SBA 48h image courtesy of CDC

Y. pestis "fried egg" on SBA at 72h image courtesy of CDC

Yersinia pestis

Culture Characteristics:
  • Growth at 22-25oC and at 35oC
  • Organism prefers 25oC, so the colonies will grow faster at this temperature
  • Growth occurs on most routine media, including sheep blood agar (SBA), chocolate agar (CHOC), MacConkey (MAC) agar, and routine blood culture media
  • Non-lactose fermenter on MAC agar
  • Growth is slower than other Enterobacteriaceae
Colony Morphology on SBA at 35oC:
  • At 24 hours, colonies are pinpoint and translucent with a gray-white color
  • Colonies take on a yellow tint as they age, after 48-72 hours, referred to as a "hammered copper" appearance
  • An irregular or "fried egg" appearance, shown in the lower image, can also be seen at 48-72 hours
Characteristic Features:
  • Growth at 22-25oC is a hallmark feature of this organism