Author/Authors :
Hamed Hamouda, Awatef Fish Diseases Department - Faculty of Fish and Fisheries Technology -Aswan University, Aswan, Egypt , Moustafa, Eman Moustafa Department of Fish Diseases and Management - Faculty of Veterinary Medicine - Kafrelsheikh University, Kafr El-Sheikh, Egypt , Mamdouh Zayed, Mohamed Department of aquaculture - Faculty of Aquatic and Fisheries Sciences - Kafr El-Sheikh University, Egypt
Abstract :
| Information about bacterial diseases from aquaculture systems at Aswan Governorate, Egypt is scarce and
old, making the interpretation, prevention and treatment of their episodes very difficult. This study aimed to shed light
on the most predominant bacterial infections in Oreochromis niloticus from Sahary fish hatchery; with special focus
on isolation, identification, and characterization of pathogenic bacteria in this cultured fish. During an epizootic;
from April to May 2018, one hundred clinically diseased Oreochromis niloticus were collected alive from the hatchery.
Diseased fish showed hemorrhagic patches distributed all over the body, detachment of scales, fin erosions, distended
abdomen and corneal opacity with exophthalmia in some cases. Collected aseptic tissue samples were cultured over
different selective differential media for phenotypic characterization. Moreover, experimental infection using the most
prevalent pathogenic bacteria (Aeromonas hydrophila) was conducted. Biochemical tests, revealed the presence of Aeromonas hydrophila, Aeromonas sobria, Pseudomonas fluorescens, Enterococcus faecalis, Staphylococcus aureus and Streptococcus
agalactiae with prevalence of 56%, 45%, 33%, 11%, 13% and 14%, respectively. Molecular identification, antimicrobial
susceptibility, multiple antibiotic resistance (MAR index) and histopathological changes induced by Aeromonas hydrophila were investigated. Aeromonas hydrophila molecularly revealed an amplified product of 356 bp size using the
16S rRNA gene and its pathogenicity is confirmed by both infectivity experiments and histopathological examination.
Aeromonas hydrophila is sensitive to Gentamicin, Ciprofloxacin, Amikacin and Nalidixic acid recording average MAR
index of 0.534 which has been indicative of isolates associated with a high risk of proceeding from environments with
usual antimicrobials use. Aeromonas hydrophila is completely resistant to Penicillin and Erythromycin.
Keywords :
Antimicrobial resistance , Experimental challenge , Histopathological alteration , Molecular characterization , Tilapia , Pathogenic bacteria
