Comparison of Biological and Genomic Characteristics Between Two Non-Intestinal <i>Salmonella Enterica</i> Serovar Enteritidis Isolates from the Same Patient

This study investigates two isolates of <i>Salmonella enterica subspecies enterica</i> serovar Enteritidis (<i>S.</i> Enteritidis), designated Sal B and Sal D, isolated from the blood and pleural fluid, respectively, of the same patient. Drug susceptibility testing revealed significant differences: Sal D exhibited greater resistance to ticarcillin/clavulanate, piperacillin/sulbactam, and ciprofloxacin compared with Sal B. Morphologically, Sal B formed rougher and drier colonies than Sal D at 37°C. Sal B demonstrated significantly stronger biofilm-forming ability and higher adhesion capacity to HaCaT cells than Sal D, whereas Sal D showed superior adaptation to acidic conditions (pH 3.0). Virulence assays indicated no significant differences between the isolates, suggesting comparable pathogenic potential. Comparative genomic analysis showed high gene content conservation but identified two nonsynonymous single-nucleotide polymorphisms (nsSNPs) and an insertion in the <i>envZ</i> and <i>siiE</i> genes. These genetic variations may account for the observed differences in drug susceptibility and biological characteristics. Collectively, these findings suggest that <i>S.</i> Enteritidis can undergo adaptive changes in response to distinct host environments, influencing drug resistance, adhesion, and acid resistance. This knowledge may inform future strategies for the treatment and prevention of <i>Salmonella</i> infections.