الفهرس 
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Abstract
Bacteriological examination of a total of 140 samples examined for the isolation of E. coli and Salmonella spp. Samples were taken from broiler chicks suffered from respiratory manifestations and/or gastrointestinal problems. The isolates were subjected for biochemical testing. The results revealed that, prevalence of E. coli (43.6%) exceeded that of Salmonella spp. (7.14%) in the examined samples.
The phenotypic detection of virulence traits of E. coli isolates revealed that 52 (85.2%) were Congo red positive (CR+) and 25 (40.98%) were hemolytic onto sheep blood agar out of 61 E. coli isolates. While 37 (60.7%) were phenotypically biofilm formmer and positive on YESCA/ CR agar.
Salmonella spp were subjected to serological identification, Out of 10 isolates, 3 serotypes were obtained. S. Kentucky was the most prevalent serotype; represented in 4 isolates (40%) followed by S. Blegdam and S.Virchow; 3 isolates (30% for each).
The in-vitro sensitivity tests were applied on 61 E. coli and 10 Salmonella spp isolates against 13 field used antimicrobial agents and MDR was detected among E. coli and Salmonella isolates) 100%) which observed as resistance for three or more antimicrobials of different categories were detected.
E. coli isolates showed high sensitivity rates to fosfomycin (85.2%), colistin sulphate (83.6%), and nitrofurantoin (80.3%). On the contrary, high resistance rates were recorded for amoxacillin clavulinic acid, apramycin and spiramycin (100%) Reduced resistences were reported for cefotaxime (98.4%), oxytetracycline (90.2%), sulph/trimethoprime (90.2%) and gentamicin (88.5%).
All the explored Salmonella isolates were resistant to apramycin, spiramycin and oxytetracycline (100%) , most of the explored isolates were highly sensitive to colistin sulphate (90%), fosfomycin and nitrofurantoin(80%) and sensitive to florofenicol 60%.
Multiplex-PCR was applied on 5 different MDR E. coli isolates for detection of 3 resistance genes (aadB, int1 and qnrS) and 3 virulence-associated genes (fimH, iss and luxS).and 5 different MDR Salmonella isolates to detect 4 genes (invA, stn, pefA and spvC). The results revealed that all the tested E. coli isolates (100%) harbored aadB, int1, qnrS, fimH, and luxS genes meanwhile 2 tested E. coli isolates (40%) harbored iss gene and all the tested Salmonella isolates (100%) harbored invA, stn and spvC genes meanwhile no isolates (0%) harbored pefA gene.
Allicin and cinnamon oils and blue green algae were tested for their antimicrobial activities against 25MDR isolates; including 15 E. coli and 10 Salmonella. Allicin oil completely inhibited the growth of all the tested E. coli and Salmonellae isolates (100%) at concentrations of 250ppm and 500ppm, cinnamon oil completely inhibited the growth of all the tested E. coli and Salmonellae isolates (100%) at concentrations of 125ppm, 63ppm while 32ppm inhibited 26.7% of E. coli and 100% of Salmonellae isolates while blue green algae at concentrations of 0.5%, 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10% had no antibacterial effect on all the tested isolates of E. coli and Salmonellae.
RT-PCR analysis was applied on 3 MDR E. coli before and after treatment with 125ppm allicin and 32ppm cinnamon to estimate variations of fimH and luxS virulence gene and Int1resistance gene. The results indicated that the gene expression for all tested genes in different bacterial isolates after treatment with allicin and cinnamon oils had decreased.