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... taxonomically belong to the genus Photobacterium that has been included in the family Vibrionaceae (Eissa et al., 2015;. Across the Red Sea, P. damselae has been involved in mortalities among marine fishes (Hashem, 2015). Photobacterium damselae subsp. ...
... piscicida is responsible for pasteurellosis in fish (Mohamed et al., 2016). Due to its growing numbers of outbreaks, this pathogen is considered a potential threat to fish abundance in the Red Sea basin (Hashem, 2015). Further, P. damselae subsp damselae has a potential zoonotic significant causing human fatal infection (Aigbivbalu & Maraqa, 2009). ...
... The necropsied fishes revealed clear signs of septicemia manifested by gills congestion and viscera, enlargement of different internal organs, and some cases exhibited liver paleness and intestine. These findings agree with those previously reported in many studies (Mustafa et al., 2014(Mustafa et al., , 2016Hashem, 2015;Mohamed et al., 2016;Mahmoud et al., 2017;Elsayed et al., 2018;Eissa et al., 2021). ...
The current study aimed to investigate the most common pathogenic
bacteria that are naturally infecting wild marine fishes collected at different
localities along the coastaline zone of Hurghada City, Egypt. A total of 300
samples of marbled spinefoot Siganus rivulatus and the Haffara Seabream
Rhabdosargus haffara were subjected to clinical and bacteriological
examinations. The examined fishes showed the characteristic clinical signs
and postmortem lesions of vibriosis and photobacteriosis. Based on the
morpho-chemical characterization, bacterial isolates retrieved from the
naturally infected fishes were identified as Vibrio spp. and Photobacterium
spp. Through sequencing 16S rRNA genes, the identities of bacterial
isolates were confirmed as V. alginolyticus, V. vulnificus, P. damselae
subsp. damselae and P. damselae subsp piscicida. Vibrio alginolyticus was
the most frequent isolated bacterial pathogen and represented 54.4% and
46.7% of the total isolates recovered from S. rivulatus and R. haffara,
respectively. Thus, the current study confirmed that Vibrio and
Photobacterium species remain the most prevalent bacterial pathogens
infecting Egyptian Red Sea fishes. From food safety perspective, these
types of infections could pose potential public health hazards
Nile tilapia, Oreochromis niloticus, one of the most important aquatic species in Egypt, has suffered intensive losses from bacterial pathogens; Aeromonas hydrophila and Photobacterium damselae during the onset of the summer season. The immune mechanisms involved in the infection of P. damselae in fish are still poorly recognized. In this study, O. niloticus intraperitoneally injected by two bacterial inocula (1.7 × 10⁵ CFU ml⁻¹ for A. hydrophila and 2 × 10⁶ CFU ml⁻¹ for P. damselae). Blood was sampled after 1, 3 and 7 days of each bacterial injection to evaluate total, differential leukocytic counts, and alterations in cellular innate immunity parameters; phagocytic activity, respiratory burst, serum lysozyme, bactericidal activity, complement system, and pro-inflammatory cytokines. Simultaneously, the mRNA expression levels of three immune-relevant genes (TLR-7, NFκB, MHC-IІα) and four pro-inflammatory cytokines related genes (IL-6, IL-8, CC-chemokine, IL-1β, and TNF-α) were evaluated in the spleen and head-kidney using q-PCR. Our data implied that tested immunological parameters and its relevant genes expression showed distinct patterns. In general, a notable increase in the leukocyte counts and innate immune responses, mainly in the respiratory burst, lysozyme, and complement (C4), but with a marked decrease in the phagocytic activity, principally on days 3 and 7 of challenge experiment. Moreover, transcript levels of immune-related genes (IL-6, IL-8, CC-chemokine, IL-1β, TLR-7, and NF-κB) were significantly down-regulated among different time points of the challenge experiment. A positive correlation was noted between gene expression obtained and tested phagocytic activity, implying that these pathogens can subvert the immune defense of the host. Together, these results symbolize the disparity in the kinetics of inherent immunity responses in peripheral blood and the molecular mechanism in immune organs used for combating these bacterial pathogens.
