الفهرس 
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Abstract
Continuous emergence of antimicrobial resistant (AMR) salmonellosis poses a threat for treatment of infectious diseases in animals and humans. Identification of factors associated with development of AMR salmonellosis and providing alternative antimicrobials to limit this threat are of a great value. Therefore, the present study aimed to estimate the prevalence of salmonellosis in diarrheic sheep and goats belonging to Giza governorate in Egypt, characterize phenotypic antimicrobial sensitivity pattern of the isolated Salmonella spp. strains, and identify the management factors associated with perpetuation of Salmonella spp pathogen among the investigated flocks. Also, the study aimed to investigate the presence of enterotoxin (stn) gene in the isolated strains and its role in development of diarrhea, and to analyze the genetic relatedness between the isolated strains and other strains retrieved from GenBank based on partial codon sequence of stn gene in order to provide a scientific basis for the implementation of practical preventive measures. Furthermore, this study aimed to investigate the ability of silver nanoparticles, Bulgarian propolis ethanolic extract and locally prepared inactivated ISA-70 mantonide adjuvanted S. Enteritidis vaccine to alternate antimicrobials to control the development of AMR problem. A cross sectional (census) survey study was conducted, and a total number of 518 diarrheic sheep and goats belonging to 7 mixed flocks of sheep and goats were enrolled from which, rectal swabs were collected and subjected to culture for Salmonella spp. The presumptive identified Salmonella colonies were biochemically identified, serotyped and molecularly confirmed to be Salmonella spp. by amplification of invA gene using polymerase chain reaction (PCR) technique. The confirmed Salmonella spp. strains were examined for their susceptibility to 10 of the most commonly used antimicrobials using minimum inhibitory concentration (MIC) and to 11 antimicrobials using disc-diffusion method. The obtained questionnaire survey data about disease occurrence were statistically analyzed using Chi-square test. Twenty Salmonella spp isolates were recovered and the overall prevalence of salmonellosis among diarrheic sheep and goats was 3.86% (20/518), and the disease prevalence per each flock ranged from 0% to 7.55%. The prevalence of serovars among the investigated animals were 1.93% for S. Mississippi, 0.39% for each of S. Durham and S. Enteritidis, and 0.19% for each of S. Ferruch, S. Paratyphi A, S. Allerton, S. Bonariensis, S. Kottbus, and S. Stanleyville. The measured multiple antimicrobial resistance index (MAR) of the recovered strains revealed that, most of strains were identified as multidrug-resistant (MDR); 100% and 70% based on MIC and disc-diffusion results, respectively. The identified disease associated factors were absence of isolation of newly-purchased animals and isolation pen for sick animals, over the counter use of antimicrobials, lack of disinfection of feeding utensils and water troughs, and presence of rodents in the feed storage area. All 20 strains carried stn gene and the partial stn codon sequence of 9 strains were deposited on GenBank and their phylogenic analysis revealed high genetic relatedness to Salmonella strains from different sources. Interestingly, the emergence of MDR Salmonella spp. poses a threat for treatment and control of salmonellosis and calls for investigation for antimicrobial alternatives. Therefore, silver nanoparticles (AgNPs) were investigated as a chemical alternative. AgNPS were synthesized by chemical reduction method. The integrated AgNPs were characterized through imaging by transmission electron microscope (TEM), fourier transform infrared spectroscopy (FTIR) analysis, and particle size distribution by dynamic light scattering (DLS) and zeta potential analyses using a nano-zetasizer. Furthermore, silver concentration was estimated by using elemental concentration of the nanoparticle solution through inductively coupled plasma atomic emission spectroscopy (ICP-AES). The in-vitro antimicrobial activity of AgNPs was investigated by estimation of minimum inhibitory concentration and minimum bactericidal concentration (MBC) for each strain using the microplate dilution method and tetrazolium salt reduction test to detect viability percentage. In -vivo treatment efficacy was assessed in mice by determining the viable count of S. Enteritidis recovered from feces and by hematologic, biochemical and histopathologic examinations to confirm that use of AgNPs has no toxic or pathologic effects and to evaluate its ability in tissue regeneration following treatment. The results of TEM, DLS, Zeta potential and FTIR revealed typical characteristics of the synthesized AgNPs. AgNPs showed antibacterial activity against all recovered strains with MIC of ≤0.02–0.313 μg/mL (mean average 0.085±0.126 μg/mL) and MBC of 0.078–1.250 μg/mL (average 0.508±0.315 μg/mL). In-vivo efficacy of AgNPs was observed by a reduction in the number of viable S. Enteritidis recovered from feces in an S. Enteritidis infected mouse model, with complete shedding stopping between treatment days 4 and 6. Hematologic, serum biochemical and histopathologic analyses proved the ability of AgNPs to suppress inflammatory reaction caused by S. Enteritidis infection. Regarding the second phytochemical alternative, the chemical composition of Bulgarian propolis ethanolic extract (EEP) was characterized using the gas chromatography-mass spectroscopy (GC-MS). The MIC and MBC of EEP were determined along with in-vivo therapeutic efficacy with reference to hematobiochemical and histological analyses. The main antibacterial compounds of EEP belonged to flavonoids, aromatic acids, and esters. Antimicrobial efficacy of EEP was detected against all strains with variable bactericidal to bacteriostatic efficacy and with an MIC of ≤0.012-6.250 mg/mL (mean 1.294 ± 1.557) and an MBC of 1.563-12.50 mg/mL (mean 4.531 ± 2.678). A therapeutic efficacy against S. Enteritidis was also noticed. Hematological and serum biochemical tests have not showed any changes due to EEP-treatment effect. In infected groups, histological examination of the liver revealed degenerative changes in hepatocytes; these changes had almost disappeared in the EEP-treated group. Thus, the ability of EEP to alternate conventional antimicrobials in both vitro and vivo was observed. Finally, an inactivated mantonide ISA-70 adjuvanted vaccine was prepared from field strain of S. Enteritidis as a biological alternative. The vaccine potency was evaluated using enzyme linked immune sorbent assay (ELISA). The vaccine achieved protection 88.88%, 77.77% and 55.55% against S. Enteritidis, S. Mississippi and S. Paratyphi A in mice. Furthermore, the prepared vaccine achieved an increase in antibody titer in the vaccinated sheep. In conclusion, the present study paved the way towards the control of antimicrobial resistant salmonellosis by elucidating the factors associated with its development and providing safe and effective antimicrobial alternatives.