Formation of viable but non-culturable state (VBNC) of Aeromonas hydrophila and its virulence in goldfish, Carassius auratus

In this study we investigated the viable but non-culturable (VBNC) state of Aeromonas hydrophila and its virulence in goldfish. Aeromonas hydrophila c ultured in a 0.35% NaCl solution at pH 7.5 and at 25 degreesC for 50 days s howed the VBNC state. In the VBNC state we were unable to detect viable bac teria by the plate count method but we did find 10(4) cells/ml by the direc t viable count microscopical method after staining with fluorescein diaceta te and ethidium bromide. The virulence comparison in goldfish showed that b acteria cultured at 25 degreesC for 1 day in a 0.35% NaCl solution were mor e virulent than bacteria cultured for 28 days. VBNC bacteria showed lower v irulence in goldfish compared to 28-day-cultured bacteria by intraperitonea l injection. The results from the study suggest that A. hydrophila can remain in the aqu atic environment for prolonged periods in the VBNC state but those cells ar e not pathogenic to goldfish.