Yersinia pestis — Key Characteristics
- Gram-negative bacilli, possible bipolar staining and a “safety pin” appearance.
- Growth is faster at 25 to 28 degrees C than at 35 to 37 degrees C.
- At 48 to 72 hours the colonies on sheep blood agar have a “fried egg” appearance.
- Catalase positive.
- Nonmotile at 35 to 37 and 25 to 28 degrees C.
- Oxidase negative.
- Urease negative.
- Nitrate-reduction negative.
- Clumped growth in broth at 25 to 28 degrees C (stalactite appearance).
Identification pitfalls to avoid
Y. pestis is included in the databases of most, but not all, enteric identification systems.
Any time a blood or sputum culture appears to be Shigella, suspect Y. pestis. Some commercial systems may confuse Acinetobacter, Shigella and hydrogen sulfide negative Salmonella with Yersinia. If you are looking for Yersinia and identify one of these organisms, review the major characteristics for Yersinia pestis.