Specific identification of Escherichia coli O157 by an immunostick method using commercially available antibodies

A sandwich enzyme-immunoassay performed on plastic sticks was developed to specifically identify Escherichia coli O157. Colonies of test bacteria grown on tryptic soy agar were suspended in phosphate-buffered saline, heated in a 100 degrees C water bath for 15 min, and incubated with the plastic sticks coated with a commercial preparation of anti-E coli O157 antibodies at 37 degrees C for 1.5 h. After incubation, the same antibodies labeled with peroxidase were used to produce the signal of antigen-antibody reaction. For 35 strains of E. coli O157 (among them 34 were E. coli O157:H7) tested, all produced strong reactions by the immunoassay. For 162 strains of E. coli with somatic antigens other than O157 and 38 strains of other genera tested, only one strain (Salmonella bietri) produced a false-positive reaction. The specificity and sensitivity of the immunostick assay were 100% (35/35) and 99.5% (199/200), respectively. The detection limit of the assay for E. coli O157:H7 (CCRC 15991) was about 10(5) CFU/ml. The method, which can be carried out within 3 h, is useful for rapid identification of suspect E. coli O157 isolated on selective media.