PCR detection of Escherichia coli O157 : H7 directly from stools: Evaluation of commercial extraction methods for purifying fecal DNA

Rapid identification of Escherichia coli O157:H7 is important for patient m anagement and for prompt epidemiological investigations. We evaluated one i n-house method and three commercially available kits for their ability to e xtract E. coli O157:H7 DNA directly from stool specimens for PCR. Of the 15 3 stool specimens tested, 107 were culture positive and 46 were culture neg ative. The sensitivities and specificities of the in-house enrichment metho d, IsoQuick kit, NucliSens kit, and QIAamp kit were comparable, as follows: 83 and 98%, 85 and 100%, 74 and 98%, and 86 and 100%, respectively. False- negative PCR results may be due to the presence of either inherent inhibito rs or small numbers of organisms. The presence of large amounts of bacteria relative to the amount of the E. coli O157:H7 target may result in the low er sensitivities of the assays. All commercial kits were rapid and easy to use, although DNA extracted with the QIAamp kit did not require further dil ution of the DNA template prior to PCR.