Background: Understanding the virulence and pathogenicity of invasive nontyphoidal Salmonella (iNTS) in children may support timely treatment and enable closer monitoring of chronic infections. iNTS epidemiology in Asia remains inadequately described. We analyzed the genetic diversity and virulence genes associated with extra-intestinal invasion in Korean children. Methods: Salmonella isolates from children < 18 yrs of age diagnosed with moderate-tosevere salmonellosis between January 2019 and December 2021 were subjected to antibiotic susceptibility testing and whole-genome sequencing. Results: In total, 58 cases were included. We identified 20 serotypes, the most prevalent being Salmonella Enteritidis (N = 21), followed by Infantis (N = 6), I 4,[5],12:i:- (N = 5), and Bareilly (N = 5). Extra-intestinal invasion occurred in 12 (20.7%) cases involving Salmonella Oranienburg (2/2), Give (1/1), Javiana (1/1), Paratyphi B var. L(+) tartrate+ (1/1), Schwarzengrund (1/1), Singapore (1/1), Montevideo (1/2), Saintpaul (1/2), I 4:b:- (1/2), Infantis (1/6), and Enteritidis (1/21). While the numbers of total virulence genes and genes belonging to major virulence categories did not significantly differ between iNTS and noniNTS, several genetic factors, including Salmonella pathogenicity island (SPI)-1 (P = 0.039), SPI-2 (P = 0.020), SPI-5 (P = 0.014), SPI-13 (P = 0.010), cytolethal distending toxin-related genes (P = 1.4 × 10 –4 ), fepC (P = 0.021), and tcpC (P = 0.040) were more frequent in invasive isolates. Conclusions Salmonella Enteritidis-ST11 predominated in infections among Korean children, but invasive isolates were rare. Early detection of genetic factors associated with extra-intestinal invasion will be helpful for prompt and appropriate treatment.

Salmonella species are among the major pathogens that cause foodborne illness outbreaks. In this study, we aimed to develop a loop-mediated isothermal amplification (LAMP) assay for the rapid and sensitive detection of Salmonella species. We designed LAMP primers targeting the hilA gene as a universal marker of Salmonella species. A total of seven Salmonella species strains and 11 non-Salmonella pathogen strains from eight different genera were used in this study. All Salmonella strains showed positive amplification signals with the Salmonella LAMP assay; however, there was no non-specific amplification signal for the non-Salmonella strains. The detection limit was 100 femtograms (20 copies per reaction), which was ~1,000 times more sensitive than the detection limits of the conventional polymerase chain reaction (PCR) assay (100 pg). The reaction time for a positive amplification signal was less than 20 minutes, which was less than one-third the time taken while using conventional PCR. In conclusion, our Salmonella LAMP assay accurately detected Salmonella species with a higher degree of sensitivity and greater rapidity than the conventional PCR assay, and it may be suitable for point-of-care testing in the field.