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Development and Evaluation of Solid Media to Identify VTEC and Detect Verotoxin in Clinical and Food Samples

Institutions
Laboratory of the Government Chemist, UK
Start date
1996
End date
1999
Objective
The aim of the project was to develop a rapid and low cost assay for the sensitive detection of verotoxin and all verotoxin producing E. coli, by:
  • development and evaluation of a method of immunologically detecting viable verotoxin producing bacteria, using solid media containing novel supplements
  • development of a system for the in vitro detection of the biological activity of verotoxin 1 and 2
More information
Current methods have difficulty in detecting VTEC strains outside specific serogroups.

The most common serogroup associated with human infection is E. coli O157:H7, although a number of other serogroups have also been implicated in disease.

The majority of identification protocols involve either exploitation of the unique biological characteristics of E. coli O157:H7 or immunological detection of serogroup-specific antigens.

Direct methods of detecting verotoxin are often slow, such as the vero-cell assay, or lack sensitivity and specificity, such as enzyme-linked immunosorbant assay (ELISA) techniques.

DNA based methods have been developed to detect VTEC contamination. Although these methods are sensitive and highly specific, they detect the ability to produce toxin rather than the actual presence of the toxin or viable toxin-producing organisms.

In order to increase sensitivity, current techniques rely on an initial enrichment culture to increase the numbers of target organisms.

However, the selective media used to isolate the potentially low numbers of VTEC present in mixed populations of bacteria were originally developed for the isolation of O157:H7 strains, and have since been demonstrated to be toxic to stressed cells.

In addition, such selective media are not favourable for the growth of some non-O157 verocytotoxin producing serogroups.

Standard selective methods also involve growth at 44°C, and such conditions may be non-permissive for some non-O157 VTECs.

An additional problem with detection of VTEC in clinical samples is the general absence of organisms in samples obtained from patients, 3-5 days after the onset of symptoms.

In such samples, being able to detect verotoxin itself would be a significant advantage.

With the increasing significance of VTEC other than O157 in foodborne illnesses reported from other countries, there is a need for a rapid yet sensitive, generic detection system able to identify the presence of either verotoxin producing bacteria or their toxins.

Find more about this project and other FSA food safety-related projects at the Food Standards Agency Research webpage.

Funding Source
Food Standards Agency
Project number
B11004
Categories
Escherichia coli
Natural Toxins