Outbreaks Spur Rapid STEC Tests

During development of the STEC suite, DuPont Qualicon considered inserting an immunomagnetic separation step prior to PCR to concentrate the six serogroups. This option was not included in the final protocol due to several inherent risks, including the potential for introducing operator error and the potential for false negative results due to interference from food debris and/or microbial effects.

A challenge for all non-O157 STEC detection methods is reliable confirmation. Isolation of E. coli O157:H7 is readily achievable because most serotypes have common phenotypic characteristics, such as sorbitol fermentation and telluride resistance. Non-O157 STEC, however, do not have specific characteristics in common that distinguish them from each other or from non-pathogenic E. coli.

The FSIS reference method uses an IMS step after PCR to concentrate cells in presumptive positive samples before streaking onto plates. However, at the time of this writing, commercial beads are not readily available for two of the serogroups—O45 and O121—so additional culture steps must be used for these. The confirmation procedure described in the FSIS Microbiology

Laboratory Guidebook, which was revised in November 2011 to include an acid treatment step, shows indications of better recovery.

What’s Next?

Many factors will influence food safety diagnostic needs in the future, including consumer and media pressure, globalization, and economics, to name just a few.

Increasing regulations will certainly have a major impact on how food companies operate. They will also drive the need for new tests that will help make it faster, easier, and more convenient for food companies to meet these new directives.

The evolution of our diet, with an increased emphasis on convenience foods, fresh foods, and “natural” foods, all of which have relatively short shelf lives, is also sure to place new demands on food safety testing.

Barbara Robleto is communications manager at DuPont Qualicon. She can be contacted at [email protected].