Question

Which of the following reagent is used in the presumptive determination of somatic cells in mastitic milk?

• A. Potassium dichromate
• B. Hydrogen peroxide
• C. Silver nitrate
• D. Sodium lauryl sulphate

Hint:

Somatic Cell Gelation Mechanism:
Anionic Detergent (Sodium Lauryl Sulphate) $+$ Somatic Cell DNA $\rightarrow$ Viscous Gel.
More Gel $=$ Higher Somatic Cell Count $=$ Severe Mastitis.

Answer 1

The Correct Option is D

Step 1: Understanding the Concept:
Mastitis is an inflammatory infection of the mammary gland that leads to a significant increase in the somatic cell count (SCC) in milk.
Somatic cells consist primarily of white blood cells (leukocytes) and epithelial cells.
A rapid, presumptive cow-side test for mastitis is the California Mastitis Test (CMT), which estimates somatic cell levels based on chemical reaction.
Detailed Explanation:
The active ingredient in the CMT reagent is sodium lauryl sulphate, an anionic surfactant.
When the reagent is mixed with a milk sample:
1. The surfactant disrupts and lyses the cell membranes of the somatic cells in the milk.
2. This lysis releases the cellular DNA from the nuclei of these cells.
3. Sodium lauryl sulphate then reacts with the released DNA, causing it to polymerize and form a gel-like, viscous precipitate.
\[ \text{Somatic Cells} + \text{Sodium Lauryl Sulphate} \rightarrow \text{Cell Lysis} \rightarrow \text{DNA Gelation} \] The viscosity of the resulting mixture is directly proportional to the number of somatic cells in the milk.
Milk from a healthy udder (low SCC) remains liquid, while milk from an infected udder (high SCC) forms a thick, gelatinous slime.
Let us review the other options:
- Potassium dichromate is used as a chemical preservative for milk samples.
- Hydrogen peroxide is an oxidizing agent.
- Silver nitrate is used in chloride estimation assays.

Step 2: Final Answer:
Sodium lauryl sulphate is the reagent used to determine somatic cells in mastitic milk.