A-1 Medium

A-1 Medium is used for the detection of coliform organisms in water and food in a laboratory setting. A-1 Medium is not intended for use in the diagnosis of disease or other conditions in humans.

Since the early 1900's enumeration of coliform organisms, specifically E. coli, have been used to determine water purity. Elevated temperature and most-probable-number (MPN) methods are routinely used for analysis of water and food samples for presence of fecal coliforms. A-1 Medium was formulated to hasten E. coli recovery and reduce the incidence of false positive cultures.

In 1972 Andrews and Presnell developed A-1 Medium. This medium recovers E. coli from estuarine water in 24 hours instead of 72 hours, and in greater numbers without the pre-enrichment step. A-1 Medium can be used in a single step procedure for the detection of fecal coliforms in source water, seawater, treated wastewater, and foods. A-1 Medium conforms to standard methods for the isolation of fecal coliforms in water and foods.


Formula Liter
Enzymatic Digest of Casein 20 g
Lactose 5 g
Sodium Chloride 5 g
Salicin 0.5 g
Triton X-100 1 g

Final pH: 6.9 ± 0.2 at 25°C
Formula may be adjusted and/or supplemented as required to meet performance specifications.


  1. Dissolve 31.5 g of the medium in one liter of purified water.
  2. Heat with frequent agitation to completely dissolve the medium.
  3. Distribute into test tubes containing Durham tubes and autoclave at 121°C for 10 minutes.
  4. Autoclave at 121°C for 10 minutes.

Order Details

Product # Product Description
7601A A-1 Medium, 500 g
7601T A-1 Medium, 5 kg