Question

MicroBiology Lab Question:

BACKGROUND INFO:

Processed/ filtered juice, juice from frozen concentrate, and fresh-squeezed juice are transferred to petri dishes and then PDA (liquified Potato Dextrose Agar) is added via pour plate method. The plates are inverted one agar solidifies and stored at 30 Celsius for 48-96 hours.

QUESTION:

Online Lab Assignment covering exercises 6-4, 6-5 and 3-4, 3-5, and 3-6 Juice: After diluting various juice samples, plating, and incubating the PDA plates we did not see much microbial growth. However, we saw a star-shaped colony. Describe the identity and details of why a star-shaped colony could appear:

Answer 1

As the juice samples contain low microbial count, it is reflected on the agar plates(PDA) and does not show much growth.

Plate 2 (middle plate in the first figure) shows a star-shaped bacterial colony. This colony may belong to Actinobacillus actinomycetemcomitans. The most Actinobacillus actinomycetemcomitans form circular and convex colonies with an internal star-shaped morphology. If you look carefully at the fourth figure, the enlarged image of the plate 2. The just below the star-shaped colony.

A. actinomycetemcomitans colonies reflect pseudopod-like extensions of the bacterial colony which penetrated deep into the TSBV agar. The centre of the colonies consisted primarily of ghost-like cells, while the dense border of each colony, including the pseudopods, expressed characteristics of vital cells.