primers specific for enterohemorrhagic escherichia coli 0157 : h7 bacteria have been designed which are useful for detecting the bacteria by polymerase chain reaction methods . the primers were derived from dna sequences contained within a 60 - mda plasmid which is present in most ehec . the primers may also be used in combination with primers derived from other sequences of significance , the conserved sequences of shiga - like toxins i and ii and the eaea gene , in a single simultaneous amplification reaction to specifically identify ehec serotype 0157 .