The selective properties of this medium prevented most non-E. coli organisms from growing, and its unique chromogenic properties differentiated the O157:H7 strain from other serotypes of E. coli (Table 1), thus increasing the specificity for detecting E. coli O157:H7 from 75.9 to 88.9%. Thus, the biochemical activity of the agar medium combined with the serological response essentially provided assurance of identification.