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Article Title

Evaluation of commercially available kits for detection of Escherichia coli O157

Abstract

In this study, four commercially available kits specific for Escherichia coli O157 and one PCR method were evaluated for their performance while applied to detect E. coli O157:H7 in foods. Using 69 pure strains, the specificity and sensitivity rates were both 100% as determined on the base of O157-antigen. While targeted on both O157 and H7 antigens, all tested kits showed 100% sensitivity rates, but specificity rates decreased to 89.6%. The detection limits of the four kits ranged from 10 3 to 10 4 CFU/mL. Both the specificity rate and sensitivity rate of the PCR method were 100%, with a detection limit of 10 3 CFU/test. This study indicated that these four commercial kits were designed only for O157 antigen of E. coli, suggesting that these kits are only useful for prescreening of O157 antigen of E. coli. Positive samples tested by the kits should be confirmed by other appropriate methods following isolation of suspect colonies. Inoculation tests revealed that one E. coli O157 cell in one gram sample could be detected following enrichment procedures. When the four kits were applied to examine market food samples, all gave different degrees of false-positive results. Hence, these kits can only be used for screening. No false-positive results were obtained by the PCR method.

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