Isolation, molecular characterization and virulence study (pathogenesis) of Photobacterium damselae subsp. damselae isolated from sea-cage and wild fishes.

Abstract

Background: Photobacterium damselae subsp. damselae is one of the most devastating zoonotic bacterial pathogen affects both fish and human health worldwide. The study aims to isolate and characterize P. damselae subsp. damselae from both wild caught and cage culture fishes. The virulence potential of P. damselae subsp. damselae on damselfish also been revealed. Methods: A total of 212 finfishes from cage culture and wild environment were collected from the south east coast of India and identified for the presence of zoonotic P. damselae subsp. damselae. Standard biochemical and molecular methods (using specific gene) were employed to identify the P. damselae subsp. damselae isolates. A total of 61 isolates were identified as P. damselae subsp. damselae. Dendogram analysis was done for selected 30 strains based on band thickness of PCR product after using IS and ERIC PCR. The data were statistically analysed by unweighted pair group method using mathematic averages (UPGMA) for numerical analysis of banding patterns. The thirty out of sixty one isolates (20% or 50%) showed their presence in both wild caught and cage cultured fishes. The isolates from the wild caught fish were tested for their virulence on damsel fish and histopathological effect also studied. Result: High prevalence of P. damselae subsp. damselae in wild caught parrot fish was noticed when compared to the cage culture fishes. The dendrogram obtained after numerical analysis with the Dice coefficient and UPGMA method shows that all patterns shared more than 50% similarity. Experimental challenge revealed that P. damselae subsp. damselae isolates from wild caught will cause severe tissue damage, abnormal behavior, clinical signs and also leads to fish mortality.