الفهرس 
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Abstract
Ascites syndrome is an economically important problem associated with high morbidity and mortality mainly affecting broiler chickens over the world. Ascites syndrome is a multifactorial etiology leading to complexity of the prevention and controlling of this disorder. Many bacterial infections are associated with ascites.
The present study focused on ascites syndrome applying advanced and conventional techniques for identification of bacterial pathogens associated with ascites in broiler chickens.
In the present study, the prevalence of ascites was studied in 500 slaughtered diseased and freshly dead broiler chickens. The results revealed that 97 chickens showed ascites with an incidence of 19.4%.
Bacteriological examination of samples collected from broiler chickens with ascites was revealed that total of 76 bacterial isolates were recovered from 70 out of 97 ascetic samples (72.2%). Sixty six percent of samples had single bacterial isolates while 6.2% had mixed infection with 2 bacterial isolates. Meanwhile 27.8% of ascetic samples showed negative bacterial isolation.
In the current study, bacteriological examination was conducted on a total of 76 bacterial isolates; either single (n=64; 84.2%) or mixed (n=12; 15.8%), which were identified by traditional methods (morphology, colonial and biochemical characteristics) as well as by Vitek2 compact system using Vitek2 ID-GN kits which is considered a rapid method for identification of 154 species of Enterobacteriaceae as well as glucose non-fermenting Gram negative organisms within 10 hrs.
The results revealed that E. coli was the most prevalent as 31 isolates (40.8%) followed by 19 Salmonella spp. (25%), 7 P. mirabilis (9.2%) then, 6 of both of P. vulgaris and C. braakii (7.9% for each), 4 P. Gallicida (5.3%) and finally 3 P. aeruginosa (3.9%). Regarding mixed isolates, all included E. coli of which 4 isolates (5.3%) were mixed with Salmonella spp. other bacteria including and one (1.3%) with each of P. mirabilis and P. vulgaris.
Serogrouping of 31 E. coli isolates revealed that 5 O-serogroups were detected while 6.5% of isolates were untyped with the available antisera. The most prevalent serogroup was O86 as 29% followed by O158 (25.8%), O114 (19.4%), O119 (12.9%) and finally O55 (6.5%).
Serotyping of 19 Salmonella isolates recovered from ascetic broiler chickens was also conducted. All isolates belonged to Salmonella enterica subsp. enterica and 4 serotypes were obtained while 21.1% of isolates were untyped with the available antisera. The most prevalent was S. Grampian represented as 36.8%, followed by S. Boecker (31.6%) and finally both of S. Muenster and S. Virchow (5.3% for each).
In the current study, all the recovered E. coli (n=31) and Salmonella (n=19) isolates were subjected to in-vitro antimicrobial susceptibility testing against 13 different antimicrobial agents for detection of the appropriate drug for treatment as well as for detection of the MDR isolates for further analyses.
Regarding E. coli isolates, the results of in-vitro antimicrobial susceptibility testing showed high resistances against all of the tested antimicrobials except colistin sulphate which showed high sensitivity. All the tested E. coli isolates (100%) were MDR and the average MDR index (MDRI) was 0.749.
Regarding Salmonella isolates, the results of in-vitro antimicrobial susceptibility testing revealed high resistances against most of the tested antimicrobials except enrofloxacin, fosfomycin, colistin sulphate, gentamicin and ciprofloxacin which showed high sensitivities. Only 15 isolates were MDR (78.9%) with MDRI of 0.514.
In the current work, PCR was applied on 5 MDR E. coli isolates; representative for all the identified serogroups to detect 4 resistance-associated genes including (sul1, tetA(A), qnrA and aac(6′)-Ib-cr) as well as 4 virulence-associated genes (iss, tsh, iutA and vat). Regarding resistance genes, the results showed that 100% of the tested E. coli isolates harbored sul1, tetA (A) and qnrA genes meanwhile no isolates harbored aac(6′)-Ib-cr gene. Meanwhile the results of virulence genes showed that 40% of tested E. coli isolates harbored iss and iutA genes while neither tsh nor vat genes was detected at any isolate.
PCR was also applied on 2 MDR Salmonella enterica isolates (Salmonella Grampian and Salmonella Boecker) to detect 4 resistance-associated genes (sul1, tetA (A), qnrA and aac(6′)-Ib-cr) as well as 4 virulence-associated genes (invA, sopB, hilA and avrA). Regarding resistance genes, the results showed that all the tested Salmonella isolates (100%) harbored sul1, tetA (A) and qnrA genes meanwhile no isolates harbored aac(6′)-Ib-cr gene. Meanwhile the results of virulence genes showed that all the selected genes were found in all tested Salmonella isolates (100%).
In the present study, cinnamon and carvacrol essential oils were tested for their antimicrobial activities against 7 MDR isolates that were used in PCR; 5 E. coli and 2 Salmonella, at concentrations of 0.01, 0.05, 0.1, 0.5 and 1% for each. Cinnamon oil showed a complete growth inhibition of all the tested E. coli and Salmonella isolates (100%) at concentrations of 1, 0.5 and 0.1% while at concentrations of 0.05 and 0.01%, no antibacterial effect was shown on any of the tested isolates but little and retarded growths were observed. Meanwhile, carvacrol oil showed complete growth inhibition of all the tested E. coli and Salmonella isolates at concentrations of 1 and 0.5% while at concentrations of 0.1, 0.05 and 0.01%, no antibacterial effect was shown on any of the tested isolates but little and retarded growths were observed.
In the current study, the quantitative RT-PCR was applied on 2 MDR E. coli serogroups O86 and O158 before and after treatment with 0.05% cinnamon and 0.1% carvacrol to estimate variations of iss virulence gene and sul1resistance gene. Moreover, RT-PCR was applied on 2 MDR Salmonella enterica isolates (S. Grampian and S. Boecker) before and after treatment with 0.05% cinnamon and 0.1% carvacrol to estimate variations of hilA virulence gene and sul1resistance gene. The results indicated that the gene expression for all tested genes in different bacterial isolates after treatment with cinnamon and carvacrol oils had decreased.