Improved microbiological techniques using the polymerase chain reaction and pulsed-field gel electrophoresis for diagnosis and follow-up of enterohaemorrhagic Escherichia coli infection

The aims of the present investigation were to evaluate the microbiological diagnostic procedures, especially polymerase chain reaction (PCR) versus cu lture and seroagglutination, in relation to the clinical features of entero haemorrhagic Escherichia coli (EHEC) infection and to study the status of E HEC in the western part of Sweden. During 1997 and 1998, stool specimens fr om 3,948 patients were analysed by PCR for the presence of EHEC with veroto xin (VT)1- and/or VT2-producing DNA sequences. The stool specimens were als o cultured for Escherichia coli O157:H7, Salmonella, Campylobacter, Shigell a and Yersinia. Fifty-five patients were positive by PCR. Thirty-nine patie nts were positive for EHEC by PCR and culture. Of these, 29 were infected w ith EHEC serogroup O157:H7 strains. All EHEC isolates were analysed by puls ed-field gel electrophoresis (PFGE); 17 different clones were identified. S tudies on the duration of the presence of EHEC in the gut showed that EHEC often disappears rather quickly, i.e. within 2 weeks. In one patient, howev er, EHEC remained for several months. In conclusion, PCR, rather than cultu re and agglutination, should be the method of choice for microbiological di agnosis of EHEC infection. PCR is more sensitive than culture for detecting EHEC in the gut.