Effect of storage and sodium chloride on excision of CTXФ or pre-CTXФ and CTXФ from Vibrio cholerae O139 strains

We examined the effect of storage and sodium chloride on excision of CTXФ or pre-CTXФ and CTXФ from Vibrio cholerae O139 strains. We found that one strain of V. cholerae O139 VO146P showed loss of the complete phage array, and other strain VO170P showed partial loss of the phage array giving rise to altered strains designated as VO146N and VO170N. Results of PCR and RFLP analysis revealed that both strains (VO146P and VO170P) possessed a single copy of pre-CTXETΦ and two copies of CTXΦ comprising CTXClassΦ and CTXCalcΦ arranged in tandem, and integrated in the large chromosome. The presence of classical ctxB was detected in CTXCalcΦ of both V. cholerae O139 strains. Nucleotide sequencing of three housekeeping genes showed no difference between parent and altered strains of V. cholerae O139.