Question

Arrange the following steps in the sequence they are used for the detection of Salmonella spp.
A. Selective enrichment
B. Non-selective enrichment
C. Selective streaking
D. Biochemical serological identification
Choose the correct answer from the options given below:

• A. B, A, C and D
• B. A, B, C and D
• C. C, D, A and B
• D. D, A, C and B

Hint:

Salmonella Detection Protocol (Mnemonic: Pre-Sel-Streak-Conf): 1. Non-selective pre-enrichment (B) $\rightarrow$ 2. Selective enrichment (A) $\rightarrow$ 3. Selective streaking (C) $\rightarrow$ 4. Biochemical/serological confirmation (D).

Answer 1

The Correct Option is A

Step 1: Understanding the Concept:
ISO 6579 FDA-BAM standardized cultural protocol for Salmonella isolation: non-selective pre-enrichment (BPW) $ ightarrow$ selective broth enrichment (RVS/MKTTn) $ ightarrow$ differential selective plating (XLD/BGA) $ ightarrow$ biochemical/serological confirmation.
Key Formula or Approach:
\[ \text{ISO 6579 Salmonella Protocol: } \mathbf{B \text{ (Pre-enrichment)}} \rightarrow \mathbf{A \text{ (Selective Broth)}} \rightarrow \mathbf{C \text{ (Selective Agar)}} \rightarrow \mathbf{D \text{ (Confirmation)}} \]

Step 2: Detailed Explanation:
Standard regulatory isolation protocol for Salmonella spp. in dairy foods (ISO 6579-1 FDA-BAM):
1. 1. Non-Selective Pre-Enrichment (B): Sample is incubated in Buffered Peptone Water (BPW) at $37^\circ ext{C}$ for 16--20 h to resuscitate sub-lethally injured cells.
2. 2. Selective Enrichment (A): Inoculate into selective liquid broths (Rappaport-Vassiliadis Soya [RVS] broth at $41.5^\circ ext{C}$ and Muller-Kauffmann Tetrathionate [MKTTn] broth) to suppress background competitor microflora.
3. 3. Selective Streaking Plating (C): Streak onto solid selective differential agar media (Xylose Lysine Deoxycholate [XLD] agar and Bismuth Sulfite Agar Brilliant Green Agar).
4. 4. Biochemical and Serological Identification (D): Confirm presumptive colonies with TSI agar, urea agar, lysine decarboxylase, and polyvalent O/H antisera.
Sequence: B $\rightarrow$ A $\rightarrow$ C $\rightarrow$ D.

Step 3: Final Answer:
Therefore, the correct sequence is B, A, C and D, matching option (A).