Yersinia pestis, the bacterium responsible for plague, has a distinct appearance when grown in laboratory conditions. Its colonies evolve in size and color over time.
Macroscopic Appearance of Yersinia pestis Colonies
When cultured, Yersinia pestis colonies exhibit specific visual characteristics that change with incubation time. These observations are crucial for identification in a laboratory setting.
Early Growth (24 Hours)
Initially, Yersinia pestis colonies are quite subtle. After approximately 24 hours of incubation, they appear:
- Color: Gray-white
- Transparency: Translucent
- Size: Generally too small to be easily seen as individual colonies, often appearing as a thin film or very tiny specks.
Mature Growth (48 Hours)
As the bacteria continue to grow, the colonies become more prominent and distinct. After about 48 hours of incubation, the colonies are typically:
- Size: Approximately 1–2 millimeters in diameter, making them much easier to observe.
- Color: Gray-white to slightly yellow
- Transparency: Opaque, meaning light does not pass through them easily.
The following table summarizes the typical appearance of Yersinia pestis colonies at different stages of growth:
| Incubation Time | Appearance | Size |
|---|---|---|
| 24 hours | Gray-white, translucent | Usually too small to be seen as individual colonies |
| 48 hours | Gray-white to slightly yellow, opaque | Approximately 1–2 mm in diameter |
These characteristic changes in size, color, and transparency aid microbiologists in identifying the presence of Yersinia pestis.
