Abstract
BackgroundWe describe a test for rapid detection of S. dysenteriae 1 in bacterial cultures and in stools, at the bedside of patients.Methodology/Principal FindingsThe 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%).ConclusionThe 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.
Highlights
Shigella is one of the most common bacterial agents of acute diarrhoea
Epidemic S. dysenteriae 1 strains resistant to ampicillin, chloramphenicol, nalidixic acid, tetracycline, trimethoprim-sulfamethoxazole, and only moderately susceptible to ciprofloxacin have been isolated with increasing frequency in Africa and Asia [10,19,20,21], while strains resistant to ciprofloxacin have recently been isolated in India and Bangladesh, reducing the availability of effective oral therapy [16,17]
We demonstrate that a dipstick based on monoclonal antibodies (mAbs) recognition of serotype 1-specific determinants carried by the LPS O-Ag, is a rapid, robust and reliable test to identify S. dysenteriae 1 in bacterial cultures when used by laboratory technicians
Summary
Shigella is one of the most common bacterial agents of acute diarrhoea. It has been estimated that 165 million cases of shigellosis occur annually worldwide, resulting in 1.1 million deaths, mainly in the Third World [1,2,3,4,5]. A severity of symptoms, high attack rate, high case-fatality rate in all age groups [6,7,8,9,10,11,12] but especially in children under 5 years [7], and various complications [13] are hallmark characteristics of infection with the Shiga bacillus This bacterium was responsible for large dysentery epidemics in Guatemala and other parts of Zaire [14], Central America [15], Bangladesh [16], Kenya [17], and recently West Africa [18] and India [19]. We describe a test for rapid detection of S. dysenteriae 1 in bacterial cultures and in stools, at the bedside of patients
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