Numerical Taxonomy of Gram-Negative, Oxidase-Positive Rods from Carcharhinid Sharks

Abstract

Clustering and ordination were used to analyze the results of a study involving phenotypic characterization (61 tests) of 197 strains of gram-negative, oxidase-positive, rod-shaped bacteria isolated from carcharhinid sharks. Also included in the data set were data for 39 reference strains representing the genera Aeromonas, Plesiomonas, and Vibrio. Unweighted pair group mathematical averaging cluster analysis resolved nine major groups of operational taxonomic units (OTUs) at simple matching coefficient (SSM) values of ≥66.5%. In turn, each group contained one or more OTU clusters (phena) at SSM values of ≥72.6%. A total of 27 phena were resolved; 14 phena were identified as Vibrio species and contained 182 of the 236 OTUs in the study. Additional phena were identified as members of the genus Aeromonas (two phena), the genus Photobacterium (three phena), the genus Alteromonas (two phena), and Plesiomonas shigelloides (one phenon). One phenon resembled descriptions of the genera Moraxella and Neisseria and Pasturella piscicida. The remaining four phena were not identified. The largest phena were identified as Vibrio damsela (52 OTUs) and Vibrio alginolyticus (48 OTUs). Vibrio carchariae and Vibrio harveyi formed subclusters (SSM values, ≥82%) within the third largest phenon (24 OTUs), which was resolved at an SSM value of ≥72.6%. Human pathogens (e.g., Vibrio cholerae) and fish pathogens (e.g., Aeromonas salmonicida, Pasteurella piscicida, and V. damsela were isolated from the sharks. Approximately 58% of all of the strains isolated and tested in this study were urease positive.