Enzyme markers for Vibrio cholerae: identification of classical, El Tor and environmental strains

Enzyme electrophoretic variants were studied in 49 strains of Vibrio cholerae using zymovar analysis. The following seven enzymes were selected for use: alanine dehydrogenase (ADH), isocitrate dehydrogenase (IDH), malate dehydrogenase (MDH), phosphoglucomutase (PGM), glucosephosphate isomerase (GPI), 6-phosphogluconate dehydrogenase (6PGDH) and glucose-6-phosphate dehydrogenase (G6PDH). The results indicated the presence of three main groups defined chiefly by their GPI and 6PGDH variants. The first group, defined by possessing the variants GPI-2 and 6PGDH-3, contained all the 01 serovar and E1T or biovar isolates from cholera cases. The second group, defined by possessing the variants GPI-3 and 6PGDH-2, contained all the 01 serovar and classical biovar isolates; the third group was heterogeneous and included the 01 serovar isolates from environmental sources as well as isolates of other serovars (the so called NAGs, non-agglutinable with 01 antisera or NCVs). It is thus now possible to separate the epidemic strains of 01 serovar from other members of this serovar isolated from the environment. Zymovar analysis deals with differences which are a direct expression of the genome and seems to be unaffected by gross phenotypic changes such as smooth-rough variation and phage resistance. It is a promising tool for investigating bacteriological and epidemiological questions, in particular the significance of an environmental reservoir of cholera.