Diversity in the arrangement of the CTX prophages in classical strains of Vibrio cholerae O1

This study reports the results of a molecular analysis of the CTX prophages in classical biotype strains of Vibrio cholerae O1 of clinical origin isolated between 1970 and 1979 in India. All strains were sensitive to group IV classical phage and polymyxin B but resistant to group 5 El Tor phage. These phenotypic traits are consistent to that exhibited by the classical biotype. PCR studies reconfirmed their biotype assignment and showed the presence of intact CTX prophages and the presence of the recently described toxin linked cryptic plasmid. Restriction fragment length polymorphism of rRNA genes and pulsed-field gel electrophoresis showed clonal diversity among the strains. The most notable observation was the finding that one strain (GP13) has three CTX prophages while another (GP147) has four CTX prophages. This is the first time heterogeneity is reported in the arrangement of the CTX prophages among classical strains of V. cholerae O1.