Characterization of Salmonella spp. in a tertiary hospital during 2019-2021 in Nanjing, China: Focusing on the clonal dissemination of Salmonella Enteritidis ST11

Abstract

Background An increasing prevalence of Salmonella spp. involving various infections in our hospital has been recently found and the characterization of these strains remained unknown. Methods A total of 38 clinical Salmonella enterica isolates were implemented for antimicrobial susceptibility testing, slide agglutination tests, and multi-locus sequence typing. WGS was performed to analyze the serovars, antibiotic-resistance genes (ARGs), virulence factors (VFs), sequence types (STs) and plasmid replicons. Phylogenetic tree was constructed to investigate the genetic relationship. Results Thirteen serovars were identified with Enteritidis (n = 19, 50.0%) being the most common, followed by Typhimurium (n = 4, 10.5%). High resistances against ampicillin (n = 27, 71.1%) and ampicillin/sulbactam (n = 24, 63.2%) were observed and 7 (18.4%) isolates were found to be multidrug resistant (MDR). Totally, 36 types of ARGs were detected with blaTEM-1B (n = 25, 65.8%) being the most frequent, and mutations in gyrA and/or parC were identified in 34 (89.5%) strains. Notably, 333 different VFs were detected, amongst them, 177 ones were shared by all isolated Salmonella strains. ST analysis identified 15 distinct STs with ST11 being the most predominant one, where a close genetic relationship between them was shown by the phylogenetic tree. Ten different plasmid replicons were found, with a dominance of IncFIB(S), IncFII(S), and IncX1 within S. Enteritidis (94.7%). Conclusions More Salmonella serovars have been identified with new molecular detection technique being developed. In addition to the high resistance and potential pathogenicity displayed by the Salmonella spp., the clonal dissemination of S. Enteritidis ST11 alerts us the necessity and urgency to implement infection and control measures.