Dipstick Test for Rapid Diagnosis of Shigella dysenteriae 1 in Bacterial Cultures and Its Potential Use on Stool Samples

by Neelam Taneja, Faridabano Nato, Sylvie Dartevelle, Jean Marie Sire, Benoit Garin, Lan Nguyen Thi Phuong, Tai The Diep, Jean Christophe Shako, François Bimet, Ingrid Filliol, Jean-Jacques Muyembe, Marie Noëlle Ungeheuer, Catherine Ottone, Philippe Sansonetti, Yves Germani

Background

We describe a test for rapid detection of S. dysenteriae 1 in bacterial cultures and in stools, at the bedside of patients.

Methodology/Principal Findings

The test is based on the detection of S. dysenteriae 1 lipopolysaccharide (LPS) using serotype 1-specific monoclonal antibodies coupled to gold particles and displayed on a one-step immunochromatographic dipstick. A concentration as low as 15 ng/ml of LPS was detected in distilled water and in reconstituted stools in 10 minutes. In distilled water and in reconstituted stools, an unequivocal positive reaction was obtained with 1.6×10⁶ CFU/ml and 4.9×10⁶ CFU/ml of S. dysenteriae 1, respectively. Optimal conditions to read the test have been determined to limit the risk of ambiguous results due to appearance of a faint yellow test band in some negative samples. The specificity was 100% when tested with a battery of Shigella and unrelated strains in culture. When tested on 328 clinical samples in India, Vietnam, Senegal and France by laboratory technicians and in Democratic Republic of Congo by a field technician, the specificity (312/316) was 98.7% (95% CI:96.6–99.6%) and the sensitivity (11/12) was 91.7% (95% CI:59.8–99.6%). Stool cultures and the immunochromatographic test showed concordant results in 98.4 % of cases (323/328) in comparative studies. Positive and negative predictive values were 73.3% (95% CI:44.8–91.1%) and 99.7% (95% CI:98–100%).

Conclusion

The initial findings presented here for a simple dipstick-based test to diagnose S. dysenteriae 1 demonstrates its promising potential to become a powerful tool for case management and epidemiological surveys.

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