Pathogenicity of newly emerged bacterial pathogens, Pseudomonas stutzeri and P. oleovorans, in the Red Sea seabream Diplodus noct

Pseudomonas is one of the most varied genera noted for its metabolism and genetic versatilities, which enable it to survive in various environmental conditions, including marine habitats. Pseudomonas species associated with fish diseases have rapidly increased, and new species are constantly being isolated. In this study, two newly emerged marine Pseudomonas pathogens, AMP-HB1 and AMP-FB1, were isolated from infected blackspot snapper, Lutjanus ehrenbergii, and blacktail butterflyfish, Chaetodon austriacus, from the National Institute of Oceanography and fisheries aquarium in Hurghada. External signs of naturally infected fish were ulcers, erosion, ophthalmitis, and cutaneous hemorrhage. The results of 16S rDNA sequencing and phylogenetic analysis confirmed that the AMP-HB1 and AMP-FB1 isolates were Pseudomonas stutzeri and P. oleovorans/pseudoalcaligenes, respectively. A challenge experiment was conducted in which the Red Sea seabream Diplodus noct were injected with a series of three different doses of 1 × 10⁷, 1.5 × 10⁸, and 3 × 10⁸ CFU from each isolate. After 7 days, the survival rates were found to be 25%, 16.6%, and 0% for P. stutzeri and 66.6%, 16.6%, and 0% for P. oleovorans, respectively. In addition, P. stutzeri exhibited multiantibiotic resistance to streptomycin, chloramphenicol, and ciprofloxacin. As well, P. oleovorans exhibited 100% resistance to the antibiotics used in this study.