Development of a Modified Enrichment Method for the Rapid Immunoassay of Escherichia Coli O157 Strains in Fresh Cut Vegetables

Development of A Modified Enrichment Method for the Rapid Immunoassay of Escherichia coli O157 Strains in Fresh Cut Vegetables

Journal of Food and Drug Analysis, Vol. 13, No. 1, 2005, Pages 64-70

Chin-Cheng Huang*, Ying-Rong Yang, Shwu-Meei Liau, Ping-Ping Chang and Chiang-Yang Cheng

Food Industry Research and Development Institute, Hsinchu, Taiwan, R.O.C.

(Received: May 18, 2004; Accepted: October 19, 2004)



Escherichia coli O157:H7 is a pathogen that colonizes human intestinal epithelial membrane and causes a characteristic lesion and severe syndromes, including diarrhea, hemorrhagic colitis, hemolytic uremic syndrome, and thrombotic thrombocytopenic purpura. It is difficult to isolate and identify this pathogen. The purpose of this research was to establish a two-stage enrichment method for the detection of E. coli O157:H7 in fresh cut vegetables. Fresh cut vegetable samples were first enriched in modified EC broth with novobiocin at 42°C for 6 hr, and then transferred to sorbitol MacConkey broth containing cefixime and tellurite at 35°C for 18 hr. Finally, the enriched broth was verified for the existence of E. coli O157 by using an automated enzyme-linked fluorescence immunoassay (mini-VIDAS) or an immunostrip test. This two-stage enrichment method would decrease the false-positive E. coli O157 tested by immunostrip or mini-VIDAS. The pathogen in food sample could be as low as 10 CFU/g and selectively enriched to 105 or 107 CFU/mL required for the detection by mini-VIDAS or immunostrip. The presence of E. coli O157:H7 in enriched broth was confirmed by multiplex polymerase chain reaction (PCR). Thus, the two-stage enrichment method can be used to rapidly screen food samples for E. coli O157.