Question

The appearance of rusty brown color on the walls of the tubes in the Hotis test for mastitic milk is mainly due to

• A. Staphylococcus aureus
• B. Streptococcus agalactiae
• C. Staphylococcus aureus and Streptococcus agalactiae
• D. Streptococcus uberis

Hint:

In the Hotis test: - Yellow spots/buttons $\rightarrow$ Streptococcus agalactiae - Rusty brown spots $\rightarrow$ Staphylococcus aureus.

Answer 1

The Correct Option is A

Step 1: Understanding the Concept:
The Hotis test is a rapid diagnostic test used to detect mastitis-causing organisms in raw milk.
It involves incubating milk with a pH indicator (bromocresol purple) and observing color changes and colony formations along the tube wall.

Step 2: Detailed Explanation:
During incubation in the Hotis test:
- Streptococcus agalactiae ferments lactose, producing acid that turns the indicator yellow. It also forms distinct, small yellow colonies or "buttons" on the bottom and sides of the tube.
- Staphylococcus aureus, on the other hand, produces a distinct reaction where the curd or bacterial colonies on the tube wall appear as a rusty brown or dark-brown color. This is due to its unique pigment production and moderate acid-digestion behavior.
- Streptococcus uberis causes a uniform yellowing or acid clotting of the milk column, but does not typically produce the specific rusty brown wall spots.
Therefore, the appearance of a rusty brown color on the walls of the tubes in the Hotis test is characteristic of Staphylococcus aureus.

Step 3: Final Answer
The correct option is (A).