A1 broth

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A1 broth is a liquid culture medium used to detect fecal coliform bacteria in foods, treated wastewater, and seawater using the most probable number (MPN) method. The recipe follows Andrews and Presnell. It is used with a Durham tube; a positive result is when a gas bubble is trapped in the tube. To prepare, dissolve the dry ingredients in 1 liter of cold distilled water, heat gently until fully dissolved, and fill 9 mL into test tubes that contain an inverted Durham tube. Sterilize at 121°C for 15 minutes in an autoclave. If you need different strengths, adjust the amount of dry medium accordingly. The final pH is 6.9 ± 0.1. Variants of this test have been used for potable water around the world, including communities in Split Lake, Manitoba; Maquehue, Chile; and in Singapore, Malaysia, and Thailand.