Detection of Escherichia coli in ready-to-eat fresh vegetables using broad-host-range recombinant phages

To construct a simple method to detect Escherichia coli in ready-to-eat fresh vegetables using broad-host-range recombinant phages.

Firstly, a gene encoding cytochrome c peroxidase (CCP) chromogenic enzyme was inserted into genomes of wild-type phages IP008 and IP052 to produce recombinant phages IP008BK and IP052BK. They were then used in the production of the chromogenic enzyme (CCP) through infection into E. coli. The method was then examined in the colorimetric detection of E. coli K12 in broth, and its appearance was confirmed by a significant change in absorbance after a few minutes of the enzyme assay. Secondly, the protocol using the recombinant phages for the detection of E. coli in vegetables, that is, lettuce and mustard greens, was investigated. A low E. coli concentration at 4 CFU per g vegetable was detected within 16·5 h that is of a shorter duration than agar plate methods and in some commonly known phage-based methods.

The existence of E. coli as a faecal contamination indicator in two types of ready-to-eat fresh vegetables, that is, lettuce and mustard greens, can be identified by the broad-host-range recombinant phages.

The method is simple and convenient since it enables the detection of E. coli without expensive apparatus. It is applicable to other types of food samples.