Dipstick for rapid diagnosis of Shigella flexneri 2a in stool.
BACKGROUND
Shigellosis or bacillary dysentery, an acute bloody diarrhoea, is a major public health burden in developing countries. In the absence of prompt and appropriate treatment, the infection is often fatal, particularly in young malnourished children. Here, we describe a new diagnostic test for rapid detection, in stool, at the bedside of patients, of Shigella flexneri 2a, the most predominant agent of the endemic form of the disease.


RESULTS
The test is based on the detection of S.flexneri 2a lipopolysaccharide (LPS) using serotype 2a-specific monoclonal antibodies coupled to gold particles and displayed on one-step immunochromatographic dipstick. A concentration as low as 20 ng/ml of LPS is detected in distilled water and in reconstituted stools in under 15 minutes. The threshold of detection corresponds to a concentration of 5x10(7) CFU/ml of S. flexneri 2a, which provides an unequivocal positive reaction in three minutes in distilled water and reconstituted stools. The specificity is 100% when tested with a battery of Shigella and unrelated strains, in culture. When tested in Vietnam, on clinical samples, the specificity and sensitivity were 99.2 and 91.5%, respectively. A decrease of the sensitivity during the evaluation on stool samples was observed after five weeks at room temperature and was due to moistening of the dipsticks caused by the humidity of the air during the fifth week of the evaluation. This drawback is now overcome by improving the packaging and providing dipsticks individually wrapped in waterproof bags.


CONCLUSIONS
This simple dipstick-bases test represents a powerful tool for case management and epidemiological surveys.
Nato
Faridabano
F
Plate-Forme 5-Production de Protéines Recombinantes et d'Anticorps, Institut Pasteur, Paris, France.
Phalipon
Armelle
A
Nguyen
Thi Lan Phuong
TL
Diep
Tai The
TT
Sansonetti
Philippe
P
Germani
Yves
Y
D000818:Animals; D000911:Antibodies, Monoclonal / Q000276:immunology; D002240:Carbohydrate Sequence; D004405:Dysentery, Bacillary / Q000175:diagnosis*; D005243:Feces / Q000382:microbiology*; D051379:Mice; D008807:Mice, Inbred BALB C; D008969:Molecular Sequence Data; D019081:O Antigens / Q000737:chemistry / Q000276:immunology; D012680:Sensitivity and Specificity; D012763:Shigella flexneri / Q000276:immunology / Q000302:isolation & purification*
D000911:Antibodies, Monoclonal; D019081:O Antigens