CHAPITRE 1 - Université de Bourgogne

For analysis, 800µL of enrichment broth is used to perform the VIDAS ESPT method
according to the manufacturer’s instructions.
The VIDAS ESPT kit includes two ready-to-use components: the Solid Phase Receptacle
(SPR) which is coated with specific E. coli O26, O103, O111, O145 and O157 phage
proteins, and a strip which contains all the wash and release solutions.
The concentration is fully automated and performed in 40 minutes using the VIDAS or mini-
VIDAS instrument. The immunoconcentrated solution is then plated on specific isolation
media.
• Isolation media
After the VIDAS ESPT protocol, 100 µL of the immunoconcentrated sample is plated on
specific media: ChromID O157 (BioMérieux, Marcy l’Etoile, France) for E. coli O157
isolation, Coli ID (BioMérieux, Marcy l’Etoile, France) and Bjorn Possé medium (Possé et
al., 2008) for the other serogroups.
• IMS
After 24hours of mTSB + novobiocine enrichment, IMS using beads from Dynal®
(Invitrogen Dynal AS, Oslo, Norway) coated with one type of specific antibodies against the
serotype of the strain used for inoculation of the sample was performed. IMS was carried out
for the five serotypes. IMS was performed according to manufacturer’s instructions. Resulting
IMS solutions were plated onto selective agar media described above. The performance of
this manual method was compared to the automated VIDAS ESPT.
RESULTS
- Sensitivity and specificity study on pure culture strains
The specificity study showed only two non specific bacteria with VIDAS ESPT assay. All
results are detailed in table 2.
Table 2: Specificity results of VIDAS ESPT on broths of STEC and non-STEC strains.
137