Key Control Points for Salmonella Detection in the Laboratory

News

News 5 6 月, 2025

1. Laboratory Setup

Salmonella detection must be conducted in a Biosafety Level 2 (BSL-2) laboratory equipped with a biosafety cabinet, especially during biochemical and serological identification of suspected colonies. Always record biosafety cabinet use to maintain traceability and ensure safety compliance.

2. Media, Reagents, and Serums

All culture media and reagents—such as BS agar, XLD agar, chromogenic media, TSI slants, biochemical kits, and polyvalent O and H antisera—must undergo quality control with standard reference strains. Since handling reference strains poses biosafety risks, all operations must be performed in a biosafety cabinet with appropriate records.

Preparation tips:

TTB and SC enrichment broths, as well as BS and XLD selective agars, are best prepared fresh before use.
Heat to boiling during preparation; pre-sterilize containers (e.g., flasks) to avoid contamination.
Protect iodine solution for TTB from light.

3. Testing Workflow

Pre-enrichment and selective enrichment are essential: These steps recover injured cells and increase detection probability, especially when Salmonella is present in low numbers among competing microflora.
Isolate multiple suspect colonies: Don’t rely solely on classic black-centered colonies. Some Salmonella strains (e.g., Arizona group) ferment lactose slowly, producing atypical colony colors. Non-Salmonella like Citrobacter freundii or Serratia liquefaciens may resemble Salmonella on chromogenic agar or show cross-reactions in serology—leading to false positives if not properly verified through full biochemical and serological profiling.
TSI slant inoculation tip: Always streak first, then stab. Reversing this order can obscure results—especially H₂S production or acid formation at the base.
Serological testing: Always include a saline control to rule out false positives.

4. Result Interpretation

Final determination must rely on a combination of biochemical test results and serotyping. Do not report positive results based on colony appearance or partial results alone.