Numerical taxonomy of Aeromonadaceae and Vibrionaceae associated with reared fish and surrounding fresh and brackish water

A numerical taxonomic study was performed on 51 isolates of gram-negative, oxidase-positive, rod-shaped, heterotrophic, facultative anaerobic bacteria isolated from aquatic samples (fresh and brackish water, eels, turbot and rainbow trout). These bacteria were compared with 28 type and references strains which included most of Aeromonas phenospecies and DNA hybridization groups, as well as strains of some arginine-positive vibrios and Plesiomonas shigelloides. The strains were characterized by 137 morphological, biochemical, physiological and nutritional tests, and data were examined by simple matching (s(SM)) and Jaccard (S-J) coefficients. Unweigthed pair group mathematical averaging cluster analysis (UPG-MA) resolved 17 groups of operational taxonomic units at S-SM values of greater than or equal to 86%. A total of 16 phena were defined. Larger phena were identified as Aeromonas jandaei and A. hydrophila. The species A. caviae, A. encheleia, A. allosaccharophila, A. salmonicida, A. sobria, A. veronii biovar veronii, A. media, Vibrio anguillarum, V. fumissii and Plesiomonas shigelloides were also represented. One phenon was identified as a member of the genus Aeromonas. Similar groupings were obtained at S-J values of greater than or equal to 79%. Virulence trials showed that most of the strains included in phena identified as A. jandaei, A. hydrophila and V. fumissii were pathogenic for eels (sample mean LD(50) of 6.5 to 7.6 (log(10))), whereas other aquatic isolates as well as reference strains from clinical origin were avirulent for fish.