Biochemical Ecology of Psychrotrophic Strains of Vibrio anguillarum Isolated from Outbreaks of Vibriosis at Low Temperature

Four strains of the fish pathogen Vibrio anguillarum have been isolated from rainbow trout (Salmo trutta), salmon (Salmo salar), coalfish (Gadus virens) and eel (Anguilla anguilla) kept captive at water temperatures of 1–4°C for aquaculture or other purposes in the vicinity of Tromsø, Norway.

Biochemically, they all closely resemble a reference strain, V. anguillarum NCMB 6. The only important exception was that our strains have lower cardinal temperatures for growth, namely 0°C (minimum), 15–18°C (optimum) and below 30°C (maximum), as opposed to an optimum of 30°C and a maximum of 30–40°C, respectively, for the reference strain.

The 4 isolates grew optimally in media containing 2% NaCl, with outer limits for growth at 0.5% and 5% NaCl. The viability was quickly lost in nutrient media without inorganic salt, in membrane-filtered seawater and by freezing or freeze-drying. The outer pH limits for growth were 5 and 9, respectively. Our strains showed enhanced anaerobic growth yields in the presence of trimethylamine oxide (TMAO).

When examined with immunochemical methods all the strains, including the reference strain, showed serological cross-reaction, but they clearly differed in antigenic structure.