Escherichia coli strains causing postweaning diarrhea (PWD) and edema disease (ED) in pigs are limited to a number of serogroups, with O8, O45, O138, O139, O141, O147, O149, and O157 being the most commonly reported worldwide. In this study, a DNA microarray based on the O-antigen-specific genes of all 8 E. coli serogroups, as well as 11 genes encoding adhesion factors and exotoxins associated with PWD and ED, was developed for the identification of related serogroups and virulence gene patterns. The microarray method was tested against 186 E. coli and Shigella O-serogroup reference strains, 13 E. coli reference strains for virulence markers, 43 E. coli clinical isolates, and 12 strains of other bacterial species and shown to be highly specific with reproducible results. The detection sensitivity was 0.1 ng of genomic DNA or 10(3) CFU per 0.3 g of porcine feces in mock samples. Seventeen porcine feces samples from local hoggeries were examined using the microarray, and the result for one sample was verified by the conventional serotyping methods. This microarray can be readily used to screen for the presence of PWD- and ED-associated E. coli in porcine feces samples.