CHAPITRE 1 - Université de Bourgogne

E. coli
strains
O26
O103
O111
O145
O157
Methods
10 5
Dilutions (CFU/mL)
10 4
10 3
VIDAS ESPT + + + -
IMS + + + -
VIDAS ESPT + + + -
IMS + + + -
VIDAS ESPT + + - -
IMS + + - -
VIDAS ESPT + + - -
IMS + - - -
VIDAS ESPT + + + -
IMS + + - -
+: all tested strains were found on the isolation media
- : at least one of the strains was not found on the isolation media
The assay performed on artificially inoculated samples (1 to 5 CFU/25g) followed by
enrichment showed high sensitivity for the isolation of STEC strains both the VIDAS ESPT
and IMS methods. Five strains of each serogroup were tested and all were isolated after
VIDAS ESPT and IMS methods. Compared to traditional IMS plates, VIDAS ESPT method
gave less background flora. VIDAS ESPT automated method greatly facilitated the recovery
of serogroups of interest.
DISCUSSION
Escherichia coli O157:H7 is the predominant and most virulent serotype of STEC.
Nevertheless, other non-O157 serogroups, including O26, O103, O111 and O145 have been
associated with occasional outbreaks human disease or sporadic cases. Sensitive and rapid
detection methods for these five serogroups are essential for the food industry to ensure a safe
food supply.
Diagnostic procedure for STEC has been developed primarily for E. coli O157:H7. All
existing validated methods research this serogroup. Detection of non-O157 STEC relies on
direct analysis of colonies on plates of limited selectivity or by immunoblotting or DNA
probing. Immuno magnetic separation (IMS) is used for selective concentration of serogroups
O26, O103, O111, O145 and O157 from pre-enriched samples to assist in plate isolation.
The VIDAS ESPT is a new method, allowing immuno-concentration of the “gang of five”
simultaneously using a new technology of phage recombinant protein. This specificity of
phage is the result of billions of years of evolutionary pressure between the phage and the host
10 2
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