Isolation and characterization of unserotypable lysogens of Vibrio cholerae phage PS166

Temperate phages of Vibrio cholerae are the major force in the emergence of newer pathogenic clones. PS166, a temperate vibriophage, has the ability to convert pathogenic biotypes of the V. Cholerae O1 serogroup. During the conversion process, PS166 also tends to produce a group of lysogens neither reported nor characterized so far. Characterization of those lysogens may provide insight into the emergence of newer pathogenic clones of V. Cholerae.

The V. cholerae eltor strain MAK757 was used to generate PS166 lysogens which were serotyped by using antisera specific to V. Cholerae O1 and O139 strains. Multiplex PCR was used to compare the status of various pathogenic markers of those lysogens. The outer membrane proteins (OMP) of the lysogens were determined by SDS-PAGE.

Temperate phage PS166 infection of V. cholerae eltor MAK757 gave rise to a new kind of lysogens termed unserotypable due to their lack of reactivity to both O1 and O139 antisera. Moreover, these lysogens displayed a new phage sensitivity profile different from both classical and parental eltor biotypes. The genetic profiles of the CTX element and VPI region of these lysogens were found to be unaltered, together with the biotype-specific markers mshA and hlyA. Though the genetic loci of major outer membrane proteins did not change after lysogenization, the outer membrane protein profile of these lysogens showed the absence of a 40-kDa band corresponding to the toxR-controlled porin, ompT.

We provide evidence for the vibriophage PS166-mediated lysogenic conversion of pathogenic cholera strains.