Development of a rapid immunochromatographic strip for detection of Escherichia coli O157.

We developed an immunochromatographic (IC) strip for the rapid detection of Escherichia coli O157 in enriched samples. Murine monoclonal antibody to E. coli O157:H7 lipopolysaccharide was conjugated with 40 nm of colloidal gold particles by the citrate method. The specificity of the IC strip was determined using 48 pure-cultured bacteria, including 32 E. coli strains and 16 non-E. coli strains. Regardless of H serotype, E. coli O157 strains produced a positive signal, whereas the others, representing 29 E. coli serotypes, did not. Among 16 non-E. coli strains, only Citrobacter amalonaticus yielded a positive signal. The sensitivity of the IC strip was determined using 10-fold diluted E. coli O157:H7, with a range of 1.8 X 10(7) to 1.8 CFU/ml in enriched raw beef. E. coli O157 could be detected at a minimum of 1.8 x 10(5) CFU/ml without enrichment and 1.8 CFU/ml after enrichment. Various samples were enriched to detect E. coli O157 using the IC strip and to isolate E. coli O157:H7 using traditional culture procedures. The IC strip test results exhibited 100% agreement with traditional methods after selective enrichment, since E. coli O157:H7 was also isolated from all the samples with positive strip test results. However, the specificity of the strip was somewhat higher with pork (98.8%) than with bovine feces (87.9%) and swine feces (93.4%). These results indicated that the IC strip exhibits high specificity and sensitivity in the detection of E. coli O157, and this assay is rapid, economical, and simple, without requirement of complicated equipment.