Genomic Diversity of Salmonella Infection from a Tertiary Hospital in China: Insights from Phenotypic and Molecular Analyses

Abstract

Background Salmonella enterica is a significant public health concern due to its ability to cause foodborne illnesses worldwide. To gain insights into the epidemiology and characteristics of Salmonella strains in China, a total of 20 Salmonella isolates were subjected to phenotypic and molecular analyses. Methods The 20 Salmonella strains were characterized through serotype identification, antimicrobial susceptibility testing (AST), biofilm formation assessment and plasmid transmission studies. Molecular characteristics and relatedness were determined using pulsed-field gel electrophoresis (PFGE) and whole genome sequencing (WGS). Additionally, SNP-based phylogenetic analysis and core genome multilocus sequence typing (cgMLST) were employed to contextualize the strains among previously sequenced S. enterica isolates in China and worldwide. Results The predominant serovar identified was Salmonella enterica serovar Enteritidis (S. Enteritidis), followed by S. Mbandaka, Thompson, Livingston, Alachua, and Infantis. The SNP-based phylogenetic analysis revealed substantial diversity among S. Enteritidis isolates, with a minimum of 32 SNPs between strains. Conversely, S. Mbandaka isolates were suspected to have originated from a single clonal expansion, displaying a difference within 6 SNPs. SNP-based phylogenetic analysis suggested S. Mbandaka clone in this study was likely to have been derived from a single source that persisted over 5 years in China. S. Mbandaka, Infantis, Livingston, and Alachua exhibited susceptibility to the tested antibiotics, while strains of S. Thompson and Enteritidis demonstrated resistance to ampicillin, quinolone, and sulfamethoxazole/trimethoprim (SMZ/TMP). Particularly concerning was the identification of one S. Enteritidis isolate carrying the highly transferable IncB/O/K/Z plasmid with blaCTX−M15, conferring cephalosporin resistance. Another isolate, harboring the mrkABCDF operon in an IncX1 plasmid, isolated from cutaneous lesions, demonstrated robust biofilm formation. Conclusions Our study emphasizes the importance of SNP-based surveillance and prompt response to Salmonella infections to protect public health. The dissemination of blaCTX−M15-harboring IncB/O/K/Z plasmid and the spread of virulent mrkABCDF operon among S. enterica in China and other global regions warrant close monitoring.