[Hemolytic-uremic syndrome caused by Escherichia coli O157:H7. Detection in direct sample of verotoxin-coding genes]

Hemorrhagic colitis is an enteritis caused by verotoxigenic strains of Escherichia coli. Conventional diagnosis requires the identification of the microorganism and the demonstration of verotoxin production. The determination of toxigenicity in isolated strains and in direct stool samples by the polymerase chain reaction (PCR) technique may simplify the diagnosis. Conventional coprocultures were performed for the detection of verotoxigenic E. coli O157:H7 from three stool samples of a patient with hemorrhagic colitis and hemolytic-uremic syndrome. The production of verotoxin was determined by cell culture and the presence of VT1 and VT2 genomic sequences by PCR. Likewise, the latter technique was applied to a direct stool sample for detection of the verotoxin codiying genes. The specificity of the amplified sequences was confirmed by enzyme restriction digestion. Escherichia coli O157:H7 was isolated in two of the three samples studied. The strains were toxigenic in the cell culture test at titers higher than 1/500 and PCR showed an amplified band of 479 pb corresponding to the VT2 codifying gene. The digestion of amplified sequences with the EcoRV enzyme led to two bands of 390 and 89 pb confirming the specificity of the results. One of the two stool samples studied directly by PCR was positive for VT2 with the result being obtained 48 hours after arrival to the laboratory. The preliminary results of this study give support to the usefulness of the polymerase chain reaction technique in the detection of verotoxin from isolated strains of Escherichia coli and in direct stool samples.