EVALUATION OF COMMERCIAL ANTISERA FOR SHIGELLA SEROGROUPING

Shigella serogrouping antisera from six companies (Becton Dickinson, D enka, Difco, Murex, Roach, and Sanofi-Pasteur) intended for the slide agglutination test and those of the Wellcolex Colour Shigella latex ag glutination test were evaluated to identify quality products for Shige lla identification, Forty-six reference Shigella strains (one for each serotype and species), 50 clinical strains (21 S. flexneri, 21 S. son nei, 4 S. dysenteriae, 4 S. boydii) representing the most prevalent sp ecies and serotypes encountered in Quebec, and 9 non-Shigella strains were tested according to the manufacturers' instructions. A 3+ reactio n (greater than or equal to 75% agglutination) was considered positive for the slide agglutination tests. Sensitivity varied from 47% (Roach ) to 94% (Difco). For the 105 strains tested, accuracy ranged from 53% (Roach) to 91% (Wellcolex). Specificity varied from 97 to 100% for gr oup A antisera, from 96 to 100% for group B antisera, from 88 to 100% for group C antisera, and from 95 to 99% for group D antisera. The cos ts of reagents required to test one strain varied from $3.50 to $13.20 (in Canadian dollars). In conclusion, Roach reagents proved to be uns atisfactory for Shigella serogrouping. Among those from the remaining companies, the Denka, Difco, and Wellcolex reagents met a performance standard of 90% accuracy.