1. Erlenmeyer flasks containing 50 mL of lactose broth.
2. Saline solution (0.9% NaCl). Autoclave at 121°C for 15 min and store at room temperature.
3. Artificial gastric fluid: 125 mM NaCl, 7 mM KCl, 45 mM NaHCO3, 3 g/L pepsin, and HCl in variable concentration between 80 and 160 mM to adjust the final pH to 2.0, 3.0, and 4.0. Prepare control gastric juice by adding 5 N NaOH up to pH 7.0. Prepare just prior to use and sterilize by filtration.
4. Artificial intestinal fluid: 0.1% w/v Pancreatin USP (ICN Biomedicals) and 0.15 % w/v bile salts (oxgall, Difco) in water. Adjust the pH to 8.0 with 5 N NaOH (see Note 1). Prepare just prior to use and sterilize by filtration.
5. pHmeter (Digimeter IV, Luftman, Argentina).
6. Water bath at 37°C with shaker (Vicking S.R.L. Shaker, Dubnoff model, Industria Argentina).
7. Sterile screwtop glass tubes.
8. Refrigerated centrifuge.
9. Diluent medium: 0.1% peptone water sterilized by autoclaving at 121°C for 15 min.
10. Lactose agar medium.
11. Anaerobic incubator.
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