In-vivo characterization of multidrug-resistant Salmonella enterica Serovar Enteritidis (SE) recovered from fertile eggs and baby chicks

The present study was conducted to isolate and characterize Salmonella spp. from hatching eggs and baby chicks. Additionally, the pathogenicity of the isolated Salmonella strains was assessed in one-day-old specific pathogen-free (SPF) chicks in-vivo. Samples from sick baby chicks from 14 broiler chicken farms (including 1 duck farm) and 150 egg batches from three breeder chicken farms were collected from 4 different governorates. Phenotypically identified Salmonella isolates were confirmed using species-specific multiplex-PCR targeting the inv -A gene for Salmonella genus, E -1 gene for Salmonella Enteritidis (SE) serovar, and Flic-C gene for Salmonella Typhimurium (ST) serovar. Confirmed SE isolates were further subjected to Random Amplified Polymorphic DNA (RAPD) fingerprinting. Phenotypic, multiplex-PCR, and RAPD fingerprinting confirmed six isolates (42.9%) from broiler chicken farms and two isolates from hatching egg batches (1.33%) as SE, of which eight were multidrug-resistant (MDR) strains with 0.214-0.786 MDR indices. In-vivo pathogenicity of selected multidrug-resistant (MDR) SE isolates was evaluated in one-day-old SPF chicks. Despite minor phenotypic diversity, most SE strains were highly invasive with variable mortality (50-100%). Interestingly, the lowest MDR indices were associated with high virulence in SE strains (mortality ≥85%) and vice versa. The study results showed the presence of SE in poultry in Egypt. The uncontrolled usage of antibiotics in poultry could be the reason for the increased prevalence of MDR Salmonella spp., which may limit Salmonella control measures and threaten public health.