Genetic relationships between clinical and environmental Vibrio cholerae isolates based on multilocus enzyme electrophoresis

A total of 107 isolates of Vibrio cholerae, including 29 strains belonging to serogroup O139, were studied using multilocus enzyme electrophoresis (ML EE) to determine allelic variation in 15 housekeeping enzyme loci. All loci were polymorphic and 99 electrophoretic types (ETs) were identified from t he total sample. No significant clustering of isolates was detected in the dendrogram generated from a matrix of coefficients of distances with respec t to serogroup, biotype or country of isolation. The mean genetic diversity of this V. cholerae population (H = 0.50) was higher than reported previou sly. Linkage disequilibrium analysis of the MLEE data showed a clonal struc ture for the entire population, but not in some of the population subgroups studied. This suggests an epidemic population structure. The results showe d that the O139 strains were not clustered in a unique ET, in contrast to p revious MLEE studies. This higher genetic variation of the O139 serogroup i s concordant with ribotyping studies. The results also confirm that the O13 9 and O1 EITor isolates are genetically more closely related to each other than to all the other subpopulations of V. cholerae studied.