Yersinia pestis

Gram Stain of Yersinia pestis


  • Biosafety Level 2 for processing clinical specimens.
  • Biosafety Level 3 practices for all culture manipulations that might produce aerosols.

Key Characteristics

  • Gram-negative bacillus
  • Grows at 35-37C, faster at room temperature.
  • Catalase positive
  • Non-motile (37C and room temperature). Note: Y. pestis is the only species of Yersinia that is non-motile at room temperature.
  • Oxidase negative
  • Biochemical characteristics: Included in the database of most enteric identification systems, but an identification of Y. pestis must be considered presumptive until confirmed by a reference laboratory.

Colony Characteristics:

  • Grows well on most non-selective standard laboratory media (ie. sheep blood, chocolate and tryptic soy agars). Pinpoint, gray-white, non-hemolytic at 24 hrs, by 48 hrs, colonies resemble typical enteric bacteria. After 48-72 hrs, gray-white to slightly yellow opague raised, irregular ““fried egg” appearance; alternatively colonies may have a “hammered copper” shiny surface.
  • Grows more slowly than other Enterobacteriaceae at 35-37C, but faster than most at room temperature.
  • Grows on MacConkey agar appearing as small non-lactose-fermenting colonies.
  • In BHI or other enriched broth, undisturbed growth is flocculent, producing structures resembling stalactites and clumps at the side and bottom of tubes.

Microscopic Characteristics:

  • A plump, Gram-negative rod (1.0-2.0 x 0.5 µm).
  • Bipolar staining with Wayson or Wright-Giemsa stain and may occasionally be seen in Gram-stained preparations, more common in specimen material than from culture. Note: Although characteristic of Y. pestis, bipolar staining is not always observable and is not unique for Y. pestis.



Yersinia species flowchart


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