Occurrence of the Vibrio cholerae seventh pandemic VSP-I island and a new variant.

Using comparative genomics, we identified a new variant of the Vibrio Seventh Pandemic Island-I (VSP-I). Results of polymerase chain reaction (PCR) screening for both known VSP-I variants indicate that the novel variant is present only in non-O1/non-O139 strains of V. cholerae and Vibrio mimicus. Comparative genomics revealed little sequence divergence in the seventh pandemic VSP-I; however, a second insertion site located on the smaller chromosome was identified. Although the seventh pandemic VSP-I genomic island was detected in all seventh pandemic V. cholerae serogroup O1 and O139 isolates examined in this study, unique genes of the island cannot be used alone as an identifying target, because the seventh pandemic VSP-I was also present in three non-seventh pandemic strains of V. cholerae isolated from Chesapeake Bay. As an alternative, a PCR assay targeting the VC2346 gene was found to be confirmatory for seventh pandemic isolates of V. cholerae.