الفهرس 
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Abstract
In the current study bacteriological examination of samples collected from broiler chicken’s intestine and internal organs revealed that the overall isolation rate of E. coli from the intestine of apparently healthy birds were 53% (80/150). While the prevalence of isolation of avian pathogenic E. coli (APEC) from different lesions of diseased broiler were 60% (90/150). Chickens. Regards to the site of systemic isolation results showed that most of E. coli isolates were obtained from liver (32.7%) followed by heart blood (24.7%) and yolk sac (2.6%).
All the recovered E. coli isolates were subjected to the phenotypic in-vitro pathogenicity based on Congo Red binding assay, assessment of biofilm formation ability, Hemolysis assay and serum resistance assay.
CR-binding assay indicated that 52 / 80 (65%) (AFEC) isolates and 50/90 (55%) (APEC) isolates were positive.
Biofilm formation ability was detected in 35 out of 80 (43.7%) of the intestinal isolates and 30 out of 90 the systemic isolates (33.3 %) were able to generate a moderate or strong biofilm.
In this study, 75 % of the avian intestinal E. coli isolates and 90% of the avian pathogenic E. coli showed α-haemolysis on sheep blood agar 5%.
Serum resistance was seen in 32 (40%) of avian intestinal E. coli isolates and 59 (65.5%) of the systemic isolates.
Serogrouping of 28 E. coli isolates which were selected positive for all the in-vitro phenotypic virulence markers (14 AFEC and 14 APEC) revealed that the most prevalent fecal E. coli serogroups was O1 followed by O128 and O158 with the prevalence of 28.5 %, 21.5% and 14.5% respectively, While the most prevalent systemic E. coli serogroups isolated was O119 and O25 with the prevalence of 21.5% for each followed by O86 (14.5%) and O1 (7%)
Antibiogram of E. coli isolates were evaluated and the result confirmed that all the tested biofilm forming isolates (100%) either intestinal E. coli (n=25) or systemic E. coli (n=25) were resistant to three or more classes of antibiotics and were considered MDR. High resistance was recorded to amoxicillin (100% for each) and Ceftriaxone (100% for each) followed by Lincomycin (96% and 100%), Kanamycin (96% and 92%), streptomycin (96% for each) and Sulfamethoxazole/ Trimethoprim (96% and 100%), ciprofloxacin (88% and 96%), Doxycycline (88% and 76%), Colistin sulphate (80% and 68%), aztreonam (72% and 80%), Ceftazidime (68% and 80%), Amoxicillin-clavulanic acid (68% and 80%) and Cefotaxime (64% and 54%). While sensitivity was recorded toward Amikacin (80% and 76%) and Fosfomycin (52% and 60%) of the (AFEC) and (APEC) respectively.
screening of some resistance and virulence genes was investigated in 12 MDR of our isolates (six AFEC and six APEC).
Resistance genes Int1 and ampC were detected with the prevalence of 100% in both (AFEC) and (APEC) isolates while Mcr1 gene was found in 100% of APEC and (83.3%) of AFEC strains.
The intended virulence genes (fimH, iss and eaeA) were detected in all the studied isolates (100%), while (pic and tsh) genes were detected with prevalence of (16.7%) in both AFEC and APEC isolates.
In this study the antibacterial effect of two essential oils (cinnamon and carvacrol) were investigated for their antimicrobial activity against 50 MDR E. coli isolates and the result showed that they were able to completely inhibited the growth of all the tested isolates at concentration of 1% and 0.5% respectively.
Results of experimental infection proved that fecal E. coli isolates were able to produce different signs of colibacillosis in broiler chicken model under the experiment, with high re-isolation rate from different internal organs. using of amino acid mixture rich in glycine can minimize the negative effects of the experimental E. coli infection.
The immune status of the chickens under experiment evaluated by different parameters. the recorded results for some selected avian cytokines using qRT- PCR, revealed that there was fold change increasement in treated groups with amino acids rich in glycine T1: T2: T3, while There is confinement of these mediators in T4, T5 and T6 which reflect on immune response against infectious agents
Regarding phagocytic count and its mediators, there were augmentation in the cells count from in T1, T2 and T3 respectively in comparison with T4, T5 and T6 which may indicate the activation of macrophages cells by action of dietary supplementation of amino acid mixture rich in glycine.