Psychrobacters and related bacteria in freshwater fish

Three phenotypic identification systems were employed to identify 106 strai ns of gram-negative, nonmotile, aerobic bacteria obtained during iced stora ge of wild (Salmo trutta and Esox lucius) and farmed (Oncorhynchus mykiss) freshwater fish. Using diagnostic tables and computer-assisted identificati on, the isolates were Psychrobacter (64 strains), Acinetobacter (24 strains ), Moraxella (6 strains), Chryseobacterium (5 strains), Myroides odoratus ( 2 strains), Flavobacterium (1 strain), Empedobacter (1 strain), and unident ified (3 strains). Overall similarities of all strains were determined for 108 characters by numerical analysis (simple matching coefficient of simila rity [S] and clustering by unweighted pair group average linkage [UPGMA]). At the 77% similarity level, 92 strains formed nine major clusters (3 or mo re strains) and four small clusters (2 strains). Cluster 1 (25 isolates div ided into two main subclusters) could be assigned to Psychrobacter phenylpy ruvicus, clusters 2 and 3 (26 isolates) were designated as Psychrobacter im mobilis, and clusters 4 (3 isolates) and 7 (4 isolates) were identified as Psychrobacter urativorans and Psychrobacter spp., respectively. Clusters 5 (five isolates), 6 (three isolates), and 9 (five isolates) were labeled as Acinetobacter spp., Acinetobacter johnsonii, and Acinetobacter Iwoffii, res pectively. Cluster 8 (12 isolates), with a high resemblance to Thornley's p henon 4 (a heterogeneous group of bacteria isolated from poultry and relate d to Acinetobacter), remained unnamed. The restriction pattern was identica l for strains grouped into clusters 2 and 3 (P. immobilis) but was differen t for the remaining Psychrobacter isolates. A large proportion of isolates belonging to the family Moraxellaceae were closely related. Psychrobacters and A. johnsonii were present in freshly caught fish and river water. In th e latter stages of storage, P, phenylpyruvicus and acinetobacters tended to decrease, whereas P. immobilis increased.