A-1 MEDIUM

Escherichia coli is used as the indicator organism to detect the faecal contamination of water. Andrews and Presnell. devised A-1 Medium, which was capable of recovering Escherichia coli from estuarine waters in 24 hours instead of 72 hours by avoiding the pre-enrichment step as recommended by APHA. This greatly reduced the time required for the complete identification of E. coli by the elevated temperature and most probable number (MPN) methods, routinely used for water analysis. A-1 Medium substantially reduces the incidence of false positive cultures. Also, Stanbridge and Delfino found that the results obtained by using 3-hours pre-incubation step (using A-1 Medium) were statistically comparable with the two-step MPN technique for the enumeration of E. coli in chlorinated waste-water. Fast recovery of faecal coliforms from shell fish and sea water was also reported. A-1 Medium also conforms to the standard methods identified for the isolation of faecal coliforms in food, water and wastewater.

for determination of faecal coliforms in water and foods by MPN technique