Polymerase chain reaction for diagnosis of enterohemorrhagic Escherichia coli infection and hemolytic-uremic syndrome

Two pairs of oligonucleotide primers were designed to amplify fragments of the genes for Shiga-like toxin I (SLT-I) and SLT-II in a single reaction. A 370-bp segment and a 283-bp segment were amplified for SLT-I and SLT-II, respectively. The specificities of the polymerase chain reaction (PCR) amplification products were confirmed by using radioactively labeled oligonucleotide probes. SLT sequences were amplified from DNA isolated from 13 previously characterized enterohemorrhagic Escherichia coli (EHEC) strains. No amplification product was produced by using DNA from 20 non-EHEC strains. As little as one bacterial genome was detectable. PCR was then applied to DNA isolated directly from stool samples. We had to remove inhibitors of PCR that were present in lysates prepared from stool samples before amplification was achieved. First, we evaluated the sensitivity of PCR for the detection of known numbers of EHEC added to normal stools. Second, three children with SLT in their stools were shown to have SLT sequences in their stools by PCR. Two of these children had hemolytic-uremic syndrome, and a third child was asymptomatic. Stool specimens collected from another 26 asymptomatic children were negative by PCR for SLT sequences. PCR can be used to diagnose EHEC infections without prior culture of stool specimens.