genetic determinants differences between vibrio cholerae biotypes

vibrio cholerae o1 are classified into two biotypes, classical and el tor based on susceptibility to bacteriophages and some biochemical properties, each encoding a biotype-specific genetic determinants. before 1961, most epidemics had been caused by the classical biotype. however, with the passage of time, the classical biotype missed from the scenario and the el tor emerged as the major biotype causing the cholera in humans. the present cholera global pandemic is attributed to a change among seventh pandemic strains and emergence of v. cholerae o139, v. cholerae o1 el tor hybrid, and v. cholera o1 el tor with altered cholera toxin subunit b. the v. cholerae  biotypes are not only different in phenotype but also human infections caused by them are different clinically. infection with classical v. cholerae o1 more frequently produces severe infection than does el tor, suggesting that the genetic and phenotypic differences between the two biotypes may also be reflected in their pathogenic potential. considering the recent emergence of “hybrid biotype” and “el tor variant” in different areas and in our country, we reviewed differences in genetic structure of v. cholerae biotypes.