Isolation, Identification, Antimicrobial Resistance, Genotyping, and Whole-Genome Sequencing Analysis of Salmonella Enteritidis Isolated from a Food-Poisoning Incident

Salmonella enterica is a common pathogen in humans and animals that causes food poisoning and infection, threatening public health safety. We aimed to investigate the genome structure, drug resistance, virulence characteristics, and genetic relationship of a Salmonella strain isolated from patients with food poisoning. The pathogen strain 21A was collected from the feces of patients with food poisoning, and its minimum inhibitory concentration against commonly used antibiotics was determined using the strip test and Kirby-Bauer disk methods. Subsequently, WGS analysis was used to reveal the genome structural characteristics and the carrying status of resistance genes and virulence genes of strain 21A. In addition, an MLST-based minimum spanning tree and an SNP-based systematic spanning tree were constructed to investigate its genetic evolutionary characteristics. The strain 21A was identified by mass spectrometry as S. enterica, which was found to show resistance to ampicillin, piperacillin, sulbactam, levofloxacin, and ciprofloxacin. The WGS and bioinformatics analyses revealed this strain as Salmonella Enteritidis belonging to ST11, which is common in China, containing various resistance genes and significant virulence characteristics. Strain 21A was closely related to the SJTUF strains, a series strains from animal, food and clinical sources, as well as from Shanghai, China, which were located in the same evolutionary clade. According to the genetic makeup of strain 21A, the change G > A was found to be the most common variation. We have comprehensively analyzed the genomic characteristics, drug resistance phenotype, virulence phenotype, and genetic evolution relationship of S. Enteritidis strain 21A, which will contribute towards an in-depth understanding of the pathogenic mechanism of S. Enteritidis and the effective prevention and control of foodborne diseases.