Isolation and Molecular Characterization of Some Bacteria Implicated in the Seasonal Summer Mortalities of Farm-raised Oreochromis niloticus at Kafr El-Sheikh and Dakahlia Governorates

Abstract

In the last years, there were some bacterial outbreaks occurred during the summer season of farm-raised Oreochromis niloticus at Kafr El-Sheikh and Dakahlia Governorates resulting in high fish mortalities and severe economic losses in these farms. So, this study aimed to detect the causes of the summer fish mortalities in these governorates to facilitate the diagnosis methods of study pathogens. Thirty fish farms were surveyed (20 in Kafr El-Sheikh and 10 in Dakahlia). 150 examined diseased fish (five from each farm) were succumbed for bacteriological isolation and biochemical and molecular identification. LD 50 experiments were done to detect the infectivity and pathogenicity of some strains of bacterial isolates. The obtained results cleared that O. niloticus summer mortalities were caused by mixed infections with different bacterial species. The isolated bacterial species were 9 types of bacteria; 7 gram negative bacteria; 78 (30.5%) Aeromonas hydrophila, 52 (20.3%) Pseudomonas aeruginosa, 40 (15.6%) Vibrio anguillarum, 20 (7.8%) Edwardsiella tarda, 12 (4.7%) Edwardsiella ictulari, 10 (3.9%) Pseudomonas fluorescens, 7 (2.7%) Flavobacterium columnare and 2 gram positive bacteria; 30 (11.7%) Streptococcus agalactia and 7 (2.8) Enterococcus feacalis which were the most prevalent bacteria affecting fish farms and implicated in the O. niloticus seasonal summer mortalities and LD 50 experiments confirmed the pathogenicity of some isolated bacteria. From the obtained results, it could be concluded that, the main cause of summer fish mortalities in studied farms was 81.82% gram negative bacteria and 18.18% was gram positive bacteria.

Virulent and Multiple Antimicrobial Resistance <i>Aeromonas hydrophila</i> Isolated from Diseased Nile Tilapia Fish (<i>Oreochromis niloticus</i>) in Egypt with Sequencing of Some Virulence-Associated Genes

“…Moreover, A. hydrophila is the most prevalent pathogen affecting freshwater fish (Abd El-Tawab et al, 2018) . The current results showed the occurrence of A. hydrophila strains in a percentage of 53.4% that was higher than previous studies (Abd El-Kader and Mousa-Balabel, 2017) .…”

Molecular Characterization of Antimicrobial Resistance of Vibrio Species Isolated from Fish in Egypt

“…The colonies morphology, Gram staining and the biochemical profile of the detected bacteria are nearly identical to those reported by many other previous authors (Ahmed and Shoreit, 2001;Noga, 2010;Abd El-Kader and Mousa-Balabel, 2017;El-Gamal et al, 2018 andHardi et al, 2018) The antimicrobial susceptibility testing method is of major time-wise; was applied to distinguish antibiotic resistance and to decide the best treatment for a particular bacteria. Clinical microbiology relies on these techniques to select the agent of choice for a bacterial infection, and to know the local and the global epidemiology of antimicrobial sensitivity.…”

Isolation, phenotypic characterization and antibiotic susceptibility of prevalent bacterial pathogens implicating the mortality of cultured Nile tilapia, Oreochromis niloticus

“…Some of the pathogenic bacteria that can cause infection in tilapia fish include Pseudomonas spp., Aeromonas spp., Vibrio spp., Streptococcus spp., Micrococcus spp., Enterococcus spp., Plesiomonas spp., Staphylococcus spp., Moraxellaceae, and Enterobacteriaceae (Zahran et al, 2016). Aeromonas hydrophila, Pseudomonas fluorescens and Vibrio anguillarum were the most predominant bacteria that cause infection in fish farms and contributed to the O. niloticus seasonal summer mortalities (Abd El-Kader and Balabel, 2017).…”