Question

Hotis test is used for differentiating, which of the following two mastitis causing pathogens?

• A. Staphylococcus aureus from Streptococcus agalactiae
• B. Streptococcus agalactiae from Streptococcus dysgalactiae
• C. Staphylococcus aureus from Streptococcus uberis
• D. Streptococcus agalactiae from Streptococcus uberis

Hint:

In the Hotis test:
- Streptococcus agalactiae = Yellow color change with characteristic yellow spots/buttons along the side of the test tube wall.
- Streptococcus dysgalactiae = Greenish-yellow color change without wall-bound yellow spots.

Answer 1

The Correct Option is B

Step 1: Understanding the Concept:
The Hotis test is a classic rapid diagnostic method developed by Hotis and Miller in 1936.
It is used to detect and differentiate mastitis-causing streptococci, specifically focusing on the detection of Streptococcus agalactiae in milk samples.
The test relies on the metabolic activity of the bacteria when incubated in milk containing a specific pH indicator.
Detailed Explanation:
The test is conducted by adding a sterile solution of the pH indicator bromocresol purple to a milk sample, followed by incubation at $37^\circ\text{C}$ for 24 to 48 hours.
Bromocresol purple is purple at a neutral pH (around 6.8) and turns yellow under acidic conditions (below 5.2).
Streptococcus agalactiae is a highly active lactose fermenter that produces acid, causing the milk to change from purple to a yellow or yellow-green color.
Crucially, as Streptococcus agalactiae grows, it forms small clumps or colonies that adhere to the sides of the test tube.
As these colonies ferment lactose locally, they produce distinct, localized yellow spots or "buttons" along the wall of the tube, often accompanied by a yellow precipitate at the bottom.
In contrast, Streptococcus dysgalactiae produces only a slight amount of acid, which turns the milk to a light green or greenish-yellow color, but it does not form the characteristic yellow spots along the wall of the tube.
Other environmental pathogens, such as Staphylococcus aureus, can be easily distinguished by basic microbiological assays like the catalase test and Gram staining, and do not show these specific patterns in the Hotis test.
Therefore, the Hotis test is a valuable screening tool to differentiate the highly contagious mastitis pathogen Streptococcus agalactiae from the environmental pathogen Streptococcus dysgalactiae.

Step 2: Final Answer:
The Hotis test is used to differentiate Streptococcus agalactiae from Streptococcus dysgalactiae.