Desarrollo de un ensayo de PCR para detectar los genes codificadores de la toxina del cólera (ctxAB) en preparaciones del candidato vacunal vivo atenuado CV638

The live oral vaccine candidate against cholera CV638 is produced under good manufacturer practices. The active ingredient of this vaccine candidate is the genetically modified strain Vibrio cholerae (V. cholerae) 638, developed by researchers at the National Center of Scientific Research, from the strain V. cholerae serogroup O1 biotype El Tor C7258, by removing the cholera toxin genes (ctxAB). Since the strain 638 lacks these genes in its genome, the presence of ctxAB in vaccine preparations, would be given by a contamination with a toxigenic V. cholerae strain. The present study was aimed at designing a specific PCR to detect ctxAB genes in DNA isolated from preparations of the vaccine candidate CV638, artificially contaminated with toxigenic V. cholerae strain. The sensitivity of the optimized PCR assay was 1 pg of genomic DNA from toxigenic strain of V. cholerae C7258, corresponding to approximately 200 genomic copies. The sensitivity of the PCR method for detecting toxigenic strains in CV638 vaccine preparations contaminated with a toxigenic strain was ∼7 × 103 colony forming units of the toxigenic strain per dose of CV638. Once validated, this method could be used in the quality control of the production of the live vaccine candidate CV638.