Abstract
The objective of this study was to investigate the molecular characterization and antibiogram of Photobacteria damselae isolated from marine cultured fish. A total number of 578 cultured marine fish (321 Seabass Dicentrarchus labrax and 257 Seabream Sparus aurata) were obtained from Alexandria governorate farms and subjected to microbiological investigation for differentiation of Photobacteria damselae subspecies. The occurrence of Photobacteria damselae subspecies piscicida and Photobacteria damselae subspecies damselae were higher in Seabream S. aurata 44.47% and 26.46% than Seabass D. labrax 38.32% and 16.20% respectively. The seasonal prevalence was the highest during summer 23.36% and 54.2% and the lowest in winter 4.49% and 6.67% respectively. The multiplex PCR assay was used to differentiate between P. d. subsp. pisci¬cida and subsp. damselae. It was based on a pair of 16S rRNA gene- PCR primers, namely CAR-1 and CAR-2 in addition to ureC gene binding primers. The P. d. subsp. damselae strains have yielded two amplification products 267 and 448 bp. The P. d. subsp. piscicida strains showed 267 bp only. Antibiogram sensitivity showed by P. damselae subsp. piscicida and P. damselae subsp. damselae strains were sen¬sitive to Sulphamethoxazole andTrimethoprim and Florofenicol.

Key words: Photobacteriosis–Seabass-Seabream- Occurrence- Molecular-Antibiogram.