A modified version of sorbitol MacConkey medium containing cefixime and tellurite (CT-SMAC medium) was produced by adding salicin and 4-methylumbelliferyl--D-galactopyranoside to CT-SMAC medium; this medium was designated CT-SSMAC medium and was used to isolate Escherichia coli O157:H7 from radish sprouts. Of 101 non-E. coli bacteria isolated from radish sprouts that produced colorless colonies similar to colonies of E. coli O157:H7 grown on CT-SMAC medium, 92 (91%) formed colonies that were red to pink or were -galactosidase negative and colorless on CT-SSMAC medium. On the other hand, colonies of E. coli O157:H7 strains were colorless and -galactosidase positive on CT-SSMAC medium. Our results suggest that CT-SSMAC medium is more selective than CT-SMAC medium for isolating E. coli O157:H7.Sorbitol MacConkey medium (SMAC medium) (11) and sorbitol MacConkey medium containing cefixime and tellurite (CT-SMAC medium) (1, 14) were described as media that can be used for isolation of Escherichia coli O157. Recently, an optimized method for detecting verocytotoxigenic E. coli in food by using CT-SMAC medium was introduced. However, it seems that modification of CT-SMAC medium is necessary to isolate E. coli O157:H7 from radish (Raphanus sativus) sprouts. During a study of the occurrence of E. coli O157:H7 in radish sprouts grown hydroponically, many colorless colonies similar to E. coli O157:H7 colonies, which do not produce acid from sorbitol, grew on CT-SMAC medium. Sata et al. (13) found that using modified E. coli broth supplemented with novobiocin or modified Trypticase soy broth supplemented with novobiocin as a liquid enrichment medium for E. coli O157:H7 is not suitable for isolating injured E. coli O157:H7 cells from water systems. Therefore, these authors recommended that a nonselective liquid enrichment medium should be used for isolation of E. coli O157:H7 (13). From these viewpoints, the role of selective agar plates in isolating E. coli O157:H7 is very important. In this study, we investigated using a modification of CT-SMAC medium for isolation of E. coli O157:H7 from radish sprouts.The strains of E. coli O157:H7 and O157:NM (nonmotile) used in this study are listed in Table 1. Five clinical isolates from patients, six bovine fecal isolates, and eight food or environmental isolates were used. Nine strains (NIID 2, NIID 457, NIID 23, NIID 42, NIID 437, NIID 1124, NIID 1856, NIID 1646, and NIID 1496 were provided by H. Watanabe (National Institute of Infectious Diseases, Tokyo, Japan). Details concerning the E. coli O157:H7 and E. coli O157:NM strains have been described previously (13). The 101 gram-negative aerobic and facultatively anaerobic rod-shaped strains that were not E. coli strains were isolated from radish sprouts in our laboratory (Table 2). Ten lots of radish sprouts marketed in Japan were used. Samples (25 g) were incubated in 225 ml of buffered peptone water (Oxoid, Basingstoke, Hampshire, England) at 36°C for 18 h. After incubation, one loopful of each culture was spread onto CT-SMA...