الفهرس 
Chapter 1 : Introduction
Bacterial infection in Oreochromis niloticusOnly 14 pages are availabe for public view
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Abstract
Oreochromis niloticus is the main cultured freshwater fish species in Egypt. Earlier studies have reported Aeromonas hydrophila to be the most predominant Aeromonas species seen in Egyptian Tilapia aquaculture without determination the prevalence and diversity of β – lactam resistance genes associated with multi-drug resistance in Aeromonas hydrophila isolates, so 400 O.niloticus were randomly collected from two private freshwater farms at Almanzala, Dakahlia province, Egypt during summer mass mortalities of 2017 and 2018. The samples were taken from apparently septicemic lesions after clinical and postmortem examination for bacteriological examination. Total number of 250 bacterial isolates from Oreochromis niloticus and surrounding water all of obtained isolates were Gram-negative. 175 Aeromonas species were isolated from the examined O.niloticus and water where A. hydrophila and A. caviae and A.sobria were identified. Accurately 100 (57.1 %) A. hydrophila strains, and 45 (25.7%) A. sobria strains and 30 (17.1%) A.cavaie strains, 28 isolates Pseudomonas fluroscens, 20 isolates Citrobacter brakii, 17 isolates photobacterium spp and 10 isolates Vibrio fluvialis.
Our results suggest that A. hydrophila is the predominant Aeromonas spp. in cultured O.niloticus in study areas. Multiple factors are involved in the virulence processes of Aeromonas hydrophila as Aerolysin (aerA), Haemolysin (hly), Cytotoxic enterotoxin (act), Cytotonic enterotoxins- heat-stable (ast), enterotoxins- heat-labile (alt) genes .Our results suggest that act, aerA and alt are the predominant virulence genes in the isolated strains and the sensitivity of all isolated strains to different group of antibiotics including penicillins, cephalosporins, monobactams and carbapenems) was evaluated. The highest rates of resistance were to Ampicillin, Amoxicillin, Piperacillin, Carpenicillin, Ticarcillin, Cefotaxime and Cefepime. Sensitivity to Imipenem was relatively high up to 100%. Additionally resistance factors as BlaTEM, BlaSHV, and BlaCTX were evaluated through polymerase chain reaction in A.hydrophila isolates. characterization of β-lactamase genes shows that BlaTEM, BlaCTX types were predominant and BlaSHV was absent which was expected as the resistance profile of study isolates showed that they were susceptible to Imipenem. Further we evaluated the potential antibacterial and immunomodulatory roles of the acidifier, (ycaamax extract 30ml/kg of diet) and imipenime antibiotic (500mg/kg) in Oreochromis niloticus. The dietary acidifiers improved the hematological parameters, liver and kidney function, suggests dietary acidifiers in O. niloticus diet was more potant as antibacterial and immunomodulatory agent more than obtained by antibiotic.