In reversed-phase high-performance liquid chromatography (RP-HPLC):
The stationary phase is hydrophobic/non-polar (typically silica modified with bonded alkyl chains such as C18 octadecylsilane or C8).
The mobile phase is hydrophilic/polar (e.g., mixtures of water/buffer with organic modifiers like methanol or acetonitrile).
In normal-phase HPLC, the stationary phase is polar and mobile phase is non-polar.

Modified Charcoal Cefoperazone Deoxycholate Agar (mCCDA) is the internationally recommended standard selective medium (ISO 10272) for the isolation and enumeration of Campylobacter jejuni and C. coli from poultry, meat, and clinical food samples. Charcoal, ferrous sulfate, and sodium pyruvate quench toxic peroxides, while cefoperazone and amphotericin B suppress competing non-campylobacter flora.

Diagnostic identification of Salmonella within enteric bacteria relies on IMViC tests (Indole test: negative; Methyl Red: positive; Voges-Proskauer: negative), Urease test on Christensen's urea broth (Salmonella is urease-negative, differentiating it from Proteus), and TSI agar ($H_2S$ production). The Catalase test is a broad primary test used to differentiate Gram-positive cocci (Staphylococci vs Streptococci), not for identifying Salmonella species.

Chromatographic applications in food analysis:

• High-Performance Liquid Chromatography (HPLC) operates in liquid mobile phase under high pressure, making it ideal for non-volatile, thermally labile biomolecules without requiring chemical derivatization.
• It is the standard instrument for resolving small polar molecules (monosaccharides, disaccharides, organic acids, free amino acids) using refractive index (RI) or UV detection.
• In size-exclusion or ion-exchange modes, HPLC is extensively utilized for separating and purifying intact proteins, peptides, and complex polysaccharides.
• Gas chromatography (GC-MS) is restricted to volatile compounds.