الفهرس 
Parasite-related diseasesOnly 14 pages are availabe for public view
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Abstract
In clinical examination of tilapia fishes, 82 out of 200 tilapia were unhealthy showed loss of equilibrium, mild lesion, hemorrhaged or inflamed fins, bulging eyes and scale loss with red spots and deep ulcers. A total of 143 bacterial isolates were obtained from the spleen, intestine, liver, muscles, kidney and testis of 82 unhealthy tilapia fishes. In addition to 10 bacterial isolates were isolated from fish feed. The most common isolate was Aeromonas hydrophila. The identification of the selected MDR A. hydrophila was molecularly confirmed by investigation of 16S rRNA gene sequences. The susceptibility of the tested 56 A. hydrophila isolates to 25 different antimicrobial agents was conducted using disk diffusion method. The incidence of resistance to different tested antibiotics ranged between 20% (nalidixic acid) and 100% (oxacillin). For pencillins, the incidence of resistance to Oxacillin, Piperacillintazobactam and piperacillin was 100%, 84% and 43%, respectively. In case of cephalosporins, the incidence of resistance ranged between ceftizoxime (98%), ceftazidime (93%), cefotaxime (91%), ceftriaxone (89%), Cefoperazoneand Cefoprazone/sulbactam (77%) among 3rd generation cephalosporins. On the other hand, high percentages (84%) of isolates showed resistance to Cefepime (4th generation cephalosporin). Interestingly, imipenem and meropenem from carbapenems made a higher number of isolates change to sensitive accordingly the percentage of resistance declined to 48% and 55%, respectively, and 71% of isolates showed resistance to aztreonam (monobactam). The resistance of A. hydrophila to colistin sulphate (lipopeptide) was moderate (59%). However, the isolates showed sharp decline in resistance to phenicol antibiotic, chloramphenicol, which showed 25% resistance, 59% to cotrimoxazole (folate pathway inhibitor). In addition to 91% of isolates were resistant to tetracycline (from tetracyclines). The MAR index analysis revealed that all tested isolates had a very high MAR index value (> 0.2). Also, all isolates showed a high frequency of multiple drug resistance (11-20) and up to 50% of the isolates showed multiple resistance to ≥ 14 antimicrobial agents. Out of 56 multi-drug resistant (MDR) isolates, five isolates (AH1, AH3, AH37, AH44 and AH52) showed a high frequency of multiple (20) drug resistance. Only one MDRAH isolate (AH37) was selected randomly for further study. Antibacterial activity of five macroalgal species extracted by three organic solvents and nine plant oils were measured against MDRAH37. Macroalgal ethanolic extracts of Sargassum vulgare and Jania rubens showed the highest antibacterial activity at 200 µl with inhibition zone diameters of 33 and 32 mm, respectively. On the other hand, the plant oil of Nigella sativa showed the most frequently antibacterial activity (inhibition zone diameters of 25 mm at 200 µl) among all tested oils. Results revealed very low MIC values of Sargassum vulgare and Jania rubens (25 mg/ml). While Nigella sativa oil gave slightly lower activity, as it possessed MIC of 50 mg/ml against the tested isolate. Transmission electron microscope (TEM) of the MDRAH37 showed the antimicrobial effects of the two algal extracts (Sargassum vulgare and Jania rubens) and one plant oil (Nigella sativa). Generally, the treated cells showed totally deformation and exhibited severe destruction. In contrast, the intact cells had a smooth surface with overall intact morphology. Destructive effects of inhibitory agents MDRAH37 appear greatly causing firstly the rupture of cell wall that lead to the leakage of cytoplasmic contents. Deeper effects of Sargassum vulgare extract appeared as the coagulation of cell proteins, and dehydration of cytoplasm. Finally, complete discharge of cytoplasmic contents will occur.