A1 Medium, also known as A1 Broth, is used for the detection of fecal coliforms in water samples. The enumeration of coliforms, specifically Escherichia coli, has been used to determine water purity by the most-probable-number method. This medium was created to hasten the recovery time of E. coli and to reduce the number of false positive cultures. A-1 Medium can be used in a single-step procedure, also in foods, not requiring a previous enrichment step. Tryptone provides nitrogen, vitamins, minerals and aminoacids. Lactose is the carbon source and in combinationwith salicin, provides energy for organism growth. Ecosurf is a surfactant and sodium chloride supplies essential electrolytes for transport and osmotic balance. Gas production is a positive reaction indicating the presence of Coliforms. Gas may be produced inside the Durham tubes or may appear as dissolved gas that forms gas bubbles when slightly agitated.
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