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

A coagglutination test was developed for identifying suspected colonies of Vibrio cholerae serotype O1 directly from primary isolation plates. Visible agglutination occurs when V. cholerae O1 antibody attached to cell-wall protein A of Staphylococcus aureus reacts with its homologous antigen. From 314 faecal samples from clinically suspected cases of cholera, 210 colonies from thiosulphate citrate bile salts sucrose (TCBS) agar and 222 colonies from taurocholate tellurite gelatin (TTG) agar were tested as suspect V. cholerae. In each case 204 isolates were identified as V. cholerae O1 by conventional methods and also gave positive results for V. cholerae O1 in the coagglutination test; with one partial exception, no other colonies tested gave positive results. The coagglutination test is simple and inexpensive and provides a result 24 h earlier than conventional methods.