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Detection of Salmonella in Foods by the Modified 1-2 Test
4) Skim milk medium (base is commercially available; Difco, Detroit, MI)
5) Tetrathionate brilliant green broth (base is commercially available)
6) EF-18 agar (EF-18, Gelman Scientific, Montreal, Qué.)
7) Hektoen enteric agar (HEK; commercially available)
8) Bismuth sulfite agar (BIS; Difco)
9) Brillian green sulpha agar (BGS; Difco)
10) Rambach agar (RAM; BDH, Toronto)
11) Xylose-Lysine-deoxycholate agar (XLD; commercially available)
12) Colworth Stomacher 400, blender or equivalent
13) Incubators capable of maintaining 35 ± 0.5°C and 43 ± 0.5°C
7. Procedure
Each sample unit may be analyzed individually or the analytical units may be combined. Carry out the test in accordance with the following instructions:
7.1 Handling of Sample Units
7.1.1 In the laboratory prior to analysis, except for shelf-stable foods, keep sample units refrigerated (0-5°C) or frozen, depending on the nature of the product. Thaw frozen samples in a refrigerator, or under time and temperature conditions which prevent microbial growth or death.
7.1.2 Analyze sample units as soon as possible after their receipt in the laboratory.
7.2 Preparation for Analysis
7.2.1 Have ready sterile nutrient broth, buffered peptone water or skim milk medium.
7.2.2 Clean the surface of the working area with a suitable disinfectant.
7.3 Preparation of Sample
7.3.1 To ensure a truly representative analytical unit agitate liquids or free flowing materials until the contents are homogeneous. If the sample unit is a solid, obtain the analytical unit by taking a portion from several locations within the sample unit. To reduce the workload, the analytical units may be combined for analysis. It is recommended that a composite contain not more than 500 g.
7.3.2 Prepare a 1:10 dilution of the food by aseptically blending 25 g or mL (the analytical unit) into 225 ml of the required preenrichment broth, as indicated in Tables I and II.
7.3.3 Adjust the pH of the mixture, if necessary, to 6.8 ± 0.2 with 1 N NaOH or 1N HCl.
7.3.4 A positive and a negative control should be set up at the same time. It is imperative that the positive control be a motile Salmonella. Test in motility agar.
7.3.5 Incubate pre-enrichment mixture and controls for 18-24 h at 35°C.
