Detection of enterohemorrhagic escherichia coli by conventional methods versus multiplex polymerase chain reaction

ABSTRACT

Enterohemorrhagic E. coli [EHEC] cause non bloody, bloody diarrhea and hemolytic uremic syndrome [HUS] which is a major cause of acute renal failure in children. This study aimed at detection of EHEC in fecal specimens of children with bloody diarrhea, comparing the conventional methods to PCR as a gold standard method. A total of 50 stool specimens collected from children with bloody diarrhea were cultured on Sorbitol Mac Conkey agar culture [SMAC] plates as a specific medium for E. coli, O157H7, ELISA for detection of shiga toxins and multiplex PCR for detection of stx[1], stx[2] eaeA and EHEC hlyA genes. Six samples out of 50 yielded non-sorbitol fermenting colonies on SMAC, none of them gave positive agglutination with O157 H7 latex antisera. While ELISA gave two positive cases [4%] out of the 50 studied cases with one false positive result, compared to PCR which gave one positive sample [2%] for stx[2] and eaeA genes, however this sample was not one of the those which gave non sorbitol fermenting colonies on SMAC. Culture on SMAC is a simple method for screening for EHEC O157, but can not be used for identification of non O157 serotypes. ELISA is a sensitive, but less specific method for detection of STEC as it detects stx produced by other species. Multiplex PCR for detection of stx[1], stx[2] eaeA and EHEC hlyA genes, is advantageous as it rapidly detects EHEC pathogenicity factors in fecal specimens