Evaluation of a rapid and automated enzyme-linked fluorescent immunoassay for detecting Escherichia coli serogroup O157 in cheese.

The Vitek Immunodiagnostic Assay System (VI-DAS) for Escherichia coli O157, a rapid and fully automated test, was evaluated for use in detecting the foodborne pathogen E. coli O157:H7 in soft, semisoft, and hard cheeses. Sixty-five cheese samples were artificially contaminated at low (2-4 colonyforming units [cfu]/25 g) and high (7-10 cfu/25 g) levels with one of 2 strains of enterohemorrhagic E. coli O157:H7. Contamination at high levels was detected in all cheeses by VIDAS, whereas in 5 cheeses (7.7%) inoculated at low levels, contamination was not detected. In 15 additional cheeses inoculated with cold-stressed cells, both VIDAS and the Bacteriological Analytical Manual cultural assay detected all high and low levels of contamination. No false positives or interference from product background fluorescence was encountered in any of the cheeses tested by VIDAS.