الفهرس 
VibriosisOnly 14 pages are availabe for public view
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Abstract
This study was conducted of 180 fishes from six fish species of Red Sea including Lutjanus ehrenbergii (Blackspot snapper), Lethrinus borbonicus (Snubnose emperor), Siganus rivulatus (Marbled spinefoot), Rhabdosargus haffara (Haffara seabream), Scarus ghobban (Blue-barred parrotfish) and Cheilinus lunulatus (Broomtail wrasse) fishes during the period of October 2019 to March 2020.
The clinical examination of the examined fishes revealed 56.1% were clinically diseased and showed mainly septicemic clinical signs, while 43.9% of the examined fishes were apparently normal. The highest clinically diseased fish was 70% among Lutjanus ehrenbergii fish and the lowest rate was 43.3% among Lethrinus borbonicus and Cheilinus lunulatus fish
The total bacterial infections among the examined fish was 70, 43.3, 63.3, 63.3, 53.3 and 43.3% among Lutjanus ehrenbergii, Lethrinus borbonicus, Siganus rivulatus, Rhabdosargus haffara, Scarus ghobban and Cheilinus lunulatus fishes respectively.
All investigated fish species were susceptible to Vibrio alginolyticus infection, while Pseudomonas abyssi infection was reported among Lutjanus ehrenbergii, Lethrinus borbonicus, Rhabdosargus haffara and Scarus ghobban fishes only. In the other hand, Psychrobacter glacincola infection was recovered in Lutjanus ehrenbergii, Rhabdosargus haffara and Scarus ghobban fishes. The mixed bacterial infection rate was 6.7% among the infected fishes, it was reported as Vibrio and Pseudomonas infection (5.6%) and Vibrio and Psychrobacter infection (1.1%).
One hundred and thirteen (113) bacterial isolates were recovered from the liver, spleen and kidney of the examined fishes. The bacteriological identification by using phenotyping and biochemical characterizations recorded that these strains were Vibrio alginolyticus, Pseudomonas abyssi and Psychrobacter glacincola and their prevalence among the examined fish was 62%, 26.5% and 11.5% respectively. This identification was confirmed by the molecular technique based on 16S rRNA gene sequence and phylogenetic analysis, where the 16S rRNA gene sequence of the three isolates was deposited into NCBI and assigned accession number MW790239 for V. alginolyticus MR C17 strain, accession number MW788678 for P. abyssi MR M71 isolate and accession number MZ413384 for Ps. glacincola MR B62 isolate.
This study recorded novel pathogenic P. abyssi and Ps. glacincola strains which were isolated from the investigated naturally clinically diseased marine fishes or Red Sea and they were pathogenic to Rhabdosargus haffara and caused 71.4%, 70% mortality rate respectively and clinical signs in similar to that of the naturally infected fishes. While the V. alginolyticus isolate caused 80% mortality rate and also clinical signs similar to that of the naturally infected fishes
The antibiotic sensitivity study revealed that V. alginolyticus isolate were sensitive to Chloramphenicol, Tetracycline, Ciprofloxacin, and Ofloxacin. P. abyssi isolates were sensitive to Chloramphenicol, Tetracycline, Ciprofloxacin, Ofloxacin, Streptomycin, Gentamycin, Tobramycin, Amoxicillin/Clavulanic Acid, Clindamycin and Flucloxacillin. Ps. glacincola was sensitive to Amikacin, Streptomycin Ciprofloxacin, Gentamycin, Chloramphenicol, Tobramycin and Ofloxacin. This study found that the MIC of AgNPs was 8µg/mL against P. abyssi had no effect against V. alginolyticus, while the MIC of ZnO NPs against P. abyssi was15 µg/mL and against V. alginolyticus was 25 µg/mL.
The treatment of Rhabdosargus haffara experimentally challenged with P. abyssi by AgNPs at 8 µg/mL / 4 hrs/day water bath for 5 successive days revealed good and promising treatment effect and complete clinical signs recovery with 20% mortality rate comparing with 60% in the control positive group and progressive deterioration of clinical signs.