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Y. pestis image courtesy of CDC

Yersinia pestis

Clinical specimens where organism may be encountered:

  • Blood
  • Lymph node aspirate
  • Respiratory secretions

Gram stain morphology:

  • Gram-negative rod
  • Resembles other Enterobacteriaceae
  • Can form short chains
  • Gram stains performed from blood culture or other liquid media may show bipolar staining (displayed by the arrows)

Note: Use of Wright-Giemsa staining on direct specimen may enhance demonstration of characteristic bipolar staining, also referred to as "safety-pin" morphology. Use of this staining is of limited value, as the method is not very sensitive or specific.