How would you determine whether a colony was a containminant on a streak plate?
To determine whether a colony is a contaminant on a streak plate, you can follow these steps:
1. Examine the colony morphology: Carefully observe the appearance of the colony. Look for any distinguishing features such as color, shape, size, and texture. Contaminant colonies may often look different from the desired colonies.
2. Compare with reference colonies: If you have reference colonies of the desired microorganism, compare the suspect colony with the reference colonies. Look for any significant differences in morphology. If the suspect colony appears different or inconsistent with the reference colonies, it may be a contaminant.
3. Consider colony location: Take note of the location of the suspect colony on the streak plate. Contaminants often appear near the edges of the plate or in areas where there is no streaking. Desired colonies are usually arranged in a distinct pattern due to streaking, while contaminants may randomly appear elsewhere.
4. Perform Gram staining (optional): If you want to confirm the identity of the colony, perform a Gram staining procedure. This staining technique helps differentiate bacteria into Gram-positive or Gram-negative groups based on the composition of their cell walls. Comparing the staining results with known characteristics of the desired microorganism can provide further clarity.
5. Isolate and re-streak the colony (optional): To confirm whether the colony is indeed a contaminant, you can isolate it by picking it up with a sterile inoculating loop and streaking it onto a fresh agar plate. If the colony grows into a pure culture consistent with the initial observation, it is likely not a contaminant.
By combining these steps, you can evaluate whether a colony on a streak plate is a contaminant or a desired microorganism more effectively.