A new automated test on the Vidas instrument to detect Escherichia coli O157 in human stool without enrichment

Abstract number: P1765

Heskia F., Mariani-Kurkdjian P., Martin S., Rey J.F., Ait-Ifrane S., Inçaurgarat B.

Objectives: VIDAS E coli O157 Clinic is an automated ELISA test based on Phage Technology for the qualitative detection of the O157 serogroup (including H7 serotype) directly from human stool. The performance obtained with the VIDAS E coli O157 kit using human stool, without enrichment was evaluated.

Methods: Antibody-based assays can exhibit cross-reactions and non-specific binding resulting in false-positive results. To improve assay specificity, we used bacteriophage recognition elements on the solid phase (VIDAS SPR) responsible for bacterial capture during the ELISA: These recognition elements utilized by bacteriophages to specifically bind to their bacterial hosts are extremely specific as they are essential for phage propagation and survival. To process samples, stools were simply diluted in buffered peptone water. No enrichment was performed.

Detection limit and precision studies were performed on artificially spiked human stools. An interference study was performed with 18 of the more common bacteria strains responsible for diarrhoea, including other STEC serogroups (O26, O103, O111, O145). Sensitivity and specificity studies were performed on 149 natural samples routinely collected from E. coli National Reference Center in Robert Debré Hospital, Paris, France.

Results: VIDAS E coli O157 displayed a very good detection limit on human stools, i.e 4.5×103 CFU/mL. The precision study was performed according to the CLSI document EP5-A2. The total % CV observed was 11.3% for a sample around the cut-off. No interference was observed with bacteria responsible for diarrhoea tested nor with other STEC serogroups. 149 naturally positive and negative human stool samples were tested with the VIDAS E coli O157 assay. Their clinical status for E coli O157 was established following the Robert Debré laboratory algorithm. The VIDAS E coli O157 assay showed a sensitivity of 96.97% and a specificity of 97.41% in comparison to this status.

Conclusion: VIDAS E coli O157 Clinic has several advantages in comparison with classical detection of E coli O157 on SMAC culture. These advantages are processing simplicity (sample dilution, VIDAS reagents and instrument ease of use), quickness (results obtained in 1.5 hour from sample processing to final result), test sensitivity compared to culture, and ease of interpretation (automated result).

The VIDAS E coli O157 Clinic shows good sensitivity with a rapid time to result.

Session Details

Date: 10/04/2010
Time: 00:00-00:00
Session name: Abstracts 20th European Congress of Clinical Microbiology and Infectious Diseases
Location: Vienna, Austria, 10 - 13 April 2010
Presentation type:
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