Detection of cholera toxin by a highly sensitive bead-enzyme linked immunosorbent assay

A bead-enzyme linked immunosorbent assay (bead-ELISA) for detection and quantification of cholera toxin (CT) in broth cultures of Vibrio cholerae O1 has been developed. Under optimal buffer and pH conditions the bead-ELISA could consistently detect 40 pg/ml of CT. None of the ingredients of commonly used media for in vitro culture of V. cholerae O1 hindered the performance of the bead-ELISA. Evaluation of the sensitivity and specificity of the bead-ELISA against the commonly used reversed passive latex agglutination (RPLA) test for detection of CT was performed using a collection of 239 strains of V. cholerae O1 (including both biotypes and serotypes) which were examined by a gene probe encoding for the A1 subunit of CT. Although both the assays were highly specific, the bead-ELISA was more sensitive than the RPLA. Quantification of CT by the bead-ELISA revealed that the concentration of CT produced by the strains of V. cholerae O1 which were negative by the RPLA was lower than 1 ng/ml and therefore below the minimum detection ability of the RPLA. The bead-ELISA is a simple, specific and highly sensitive assay for routine detection of CT and is recommended for routine use in clinical microbiology laboratories.