To develop a probe for the detection of serogroup 0157 enterohemorrhagic Exheric&a
coli (EHEC), plasmid DNA extracts from 16 E. coli strains that hybridized with the
CVD419 probe were screened for restriction fragments present in plasmids of serogroup
0157 E. coli strains, but not in plasmids of non-0157 E. co& strains. Using a single 0157:H7
E. coli strain (63911, 10 serogroup 0157 E. coli specific fragments were then removed,
radiolabeled and hybridized (42°C) with colony blots of both groups of strains. A 2.0 kb
SmaI fragment probe WPMl) was the most specific for serogroup 0157 EHEC: Using a
larger set of 41 non-E. coli and 107 E. coii strains from human, animal and meat sources,
VPMl hybridized with all 49 serogroup 0157 EHEC strains. None of 8 enterotoxigenic E.
coli (ETEC), including serogroup 0157 strains, nor any of the 41 non-E. co& hybridized with
the VPMl probe. However, this probe hybridized with 5 of 50 non-0157 E. coli which were
verotoxin (VT) or CVD419 probe-positive. Increased hybridization stringency (45°C) reduced
the 5 false-positives to 2 negatives and 3 trace responses, which were easily
distinguishable from positive responses.