Rapid identification of Vibrio cholerae serotype O1 from primary isolation plates by a coagglutination test

This technical report describes the development and validation of a coagglutination test for rapid identification of Vibrio cholerae serotype O1 directly from primary isolation plates. The test uses Staphylococcus aureus cells coated with V. cholerae O1-specific antibodies; visible agglutination occurs when the antibody-coated bacteria react with homologous antigen from suspected colonies. The researchers tested suspected V. cholerae colonies from 314 fecal samples cultured on two selective media (TCBS and TTG agar). Of 204 isolates confirmed as V. cholerae O1 by conventional biochemical and serological methods, all 204 tested positive in the coagglutination test with colonies from both media. Six non-O1 colonies from TCBS agar and 17 of 18 non-O1 colonies from TTG agar gave negative results, with one V. mimicus strain showing weak positive reaction. The coagglutination test provides results in 18-24 hours, approximately 24 hours faster than conventional methods, while requiring minimal resources, training, and antiserum. The test demonstrated both high sensitivity and specificity, making it suitable for implementation in resource-limited laboratory settings.

Key findings

• The coagglutination test correctly identified all 204 V. cholerae O1 isolates from primary isolation plates with no false negatives
• Results were obtained in 18-24 hours, approximately one day faster than conventional identification methods
• The test showed high specificity with minimal cross-reactivity; non-O1 Vibrio species and other bacteria failed to react with the reagent
• The method is economical, requiring only 0.2 ml of antiserum per 5 ml of reagent compared to conventional slide agglutination
• The test works equally well with colonies from both TCBS and TTG selective media, making it practical for field and small laboratory use