الفهرس 
General Introduction and Aim of WorkOnly 14 pages are availabe for public view
 |  | from | 104 |  |  |
| | | from | 104 | | |
Abstract
Streptococcosis has been a serious concern for veterinary practice and public health worldwide. The aim of this study was to shed light on the predominant streptococcus species among cultured freshwater fishes (O. niloticus & C. gariepinus) in Kafr-Elshiekh fish farms, Egypt with special concern to isolation, biohemical identification and molecular identification. Antibiotic resistance genes and virulence associated genes of S. iniae isolated from cultured Nile tilapia was done also in the current study. In doing that, Out of the 300 collected fish samples, 210 samples were clinically diseased (140 O. niloticus, and 70 C. gariepinus). Samples were collected from brain, kidney, liver, spleen, skin lesion and eyes. Out of 210 clinically diseased fishes, 80 isolates of Streptococcus species were isolated (60 from Nile tilapia and 20 from catfish). A total of 41 S. iniae strains (51.25%) were isolated and biochemicaly identified; 30 (73.13%) from O. niloticus, and 11 (27.83%) from C. gariepinus. Meanwhile, 25 S. agalactiae strains (31.25%) were isolated; 20 (80%) from O. niloticus, and 5 (22%) from C. gariepinus. Besides, 14 S. dysgalactiae strains (17.5%) were isolated; 10 (71.43%) from O. niloticus, and 4 (28.57%) from C. gariepinus. Fifteen isolates (50%) were identified as S. iniae from 30 isolates by polymerase chain reaction using 16S rRNA specific primers. Sensitivity of S. iniae isolates was monitored for erythromycin, tetracycline, norfloxacin, ciprofloxacin, oxytetracycline, streptomycin, sulfamethoxazole-trimethoprim, amoxicillin, and florfenicol. S. iniae showed highly resistance to erythromycin and tetracycline. All of the tetracycline-resistant isolates contained the tet(M/O) gene, of which 3 and 2 isolates contained the tet(M) and tet(O) genes, respectively. Among the erythromycin-resistant isolates 3 contained the erm(B) gene. Molecular study revealed the presence of six virulence associated genes in the recovered S.iniae isolates. The recovered genes are scpl, simA, pdi, SagA, pgmA and cpsD, these genes were detected in7, 7,
5, 4, 3 and 9 isolates representing 46.6, 46.6, 33.3, 26.6, 20 and 60% respectively. Virulence associated genes may have a potential role in disease severity and promoting the pathogenicity of bacterial infection. The studied isolates showed multiple antibiotic resistance profile, so it may be very difficult to treat such infection, and there is a need to develop a new strategy for controlling streptococcus outbreaks in infected farms like vaccination.