Salmonellosis is an important zoonotic disease of chickens that poses a serious threat to the poultry industry in developing countries, especially in Egypt. This study aimed to isolate and identify Salmonella (S.) from commercial broiler chickens, in addition to serological and molecular evaluation of the immunocompromising effect of S. Enteritidis. Out of 246 samples collected from broiler chicken farms, the prevalence of Salmonella was 4.1% (8/192), 6.4% (2/31), (0/7), (0/7), (0/5), and (0/4) in the cecum, liver, gallbladder, air sacs, spleen, and pericardium samples, respectively. Those ten isolates were obtained from 88 broiler flocks, representing 11.36% (10/88), and all were characterized as S. Enteritidis (1,9,12:g,m). Their in-vitro antimicrobial susceptibility testing revealed high resistance (100%) to amoxicillin-clavulanic acid, streptomycin, erythromycin, clindamycin, doxycycline, fosfomycin, and sulfamethoxazole-trimethoprim. All S. Enteritidis isolates carried three virulence genes, i.e., invA, sefA, and fimH, while stn was detected in 7 isolates. Additionally, all isolates harbored Extended-spectrum β-lactamases (ESBL)-producing (blaTEM ) and sul1 antimicrobial resistance genes. Following experimental infection with an S. Enteritidis isolate in broilers at seven days old and routine vaccinations using an inactivated and live LaSota, Newcastle vaccines, severe immunocompromising effects were observed in terms of antibody response to vaccination, as well as several immune mediators such as nitric oxide, lysozyme, IFN-γ, IL-6, IL-8, and IL-10 as well as phagocytic count. In conclusion, S. Enteritidis carrying several virulence and antimicrobial resistance genes was characterized from cecal and liver samples collected from different broiler flocks. Infection with S. Enteritidis induced a prolonged inflammatory response and negatively affected the broilers’ immune response to Newcastle disease vaccination.
Key words: Salmonella Enteritidis, Antimicrobial, Immunocompromising, Broiler chickens
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