Polyphasic Taxonomy of the Genus Vibrio: Numerical Taxonomy of Vibrio cholerae, Vibrio parahaemolyticus , and Related Vibrio Species

Abstract

A set of 86 bacterial cultures, including 30 strains of Vibrio cholerae , 35 strains of V. parahaemolyticus , and 21 representative strains of Pseudomonas, Spirillum, Achromobacter, Arthrobacter , and marine Vibrio species were tested for a total of 200 characteristics. Morphological, physiological, and biochemical characteristics were included in the analysis. Overall deoxyribonucleic acid (DNA) base compositions and ultrastructure, under the electron microscope, were also examined. The taxonomic data were analyzed by computer by using numerical taxonomy programs designed to sort and cluster strains related phenetically. The V. cholerae strains formed an homogeneous cluster, sharing overall S values of ≥75%. Two strains, V. cholerae NCTC 30 and NCTC 8042, did not fall into the V. cholerae species group when tested by the hypothetical median organism calculation. No separation of “classic” V. cholerae , El Tor vibrios, and nonagglutinable vibrios was observed. These all fell into a single, relatively homogeneous, V. cholerae species cluster. V. parahaemolyticus strains, excepting 5144, 5146, and 5162, designated members of the species V. alginolyticus , clustered at S ≥80%. Characteristics uniformly present in all the Vibrio species examined are given, as are also characteristics and frequency of occurrence for V. cholerae and V. parahaemolyticus . The clusters formed in the numerical taxonomy analyses revealed similar overall DNA base compositions, with the range for the Vibrio species of 40 to 48% guanine plus cytosine. Generic level of relationship of V. cholerae and V. parahaemolyticus is considered dubious. Intra- and intergroup relationships obtained from the numerical taxonomy studies showed highly significant correlation with DNA/DNA reassociation data.