[Genomic characteristics of emerging toxigenic Salmonella enterica subsp. diarizonae 50:z52:z35/ST8433 cloning from diarrhea cases].

Abstract

To analyze the genomic and disease ecological background of two Salmonella enterica subsp. diarizonae (S.Ⅲb) isolated from two children with diarrhea. A retrospective analysis was conducted on the clinical data of two pediatric patients who presented to the gastroenterology outpatient clinic of Fudan University Affiliated Children's Hospital with symptoms of fever and diarrhea and were ultimately diagnosed with bacterial enteritis. Both patients' fecal samples tested positive for Salmonella infection. Whole-genome sequencing results indicated that the strains were all S.Ⅲb 50:z₅₂:z₃₅/ST8433, which were not recorded in domestic or international databases. Antimicrobial susceptibility testing showed that Salmonella strain isolated from Case 1 was an antibiotic-sensitive strain, susceptible to 28 antimicrobial agents; Salmonella strain isolated from Case 2 was a multidrug-resistant strain, susceptible to only 11 antimicrobial agents, and resistant to β-lactam, quinolone, and macrolide antibiotics. The strain of case 1 carried aac(6')-Iaa and quinolone parC(T57S) resistance genes. The strain of Case 2 had a unique chromosome encoding the type Ⅲ secretion systems (T3SS) of Yersinia enterocolitica, and the number of invasion protein genes and typhoid toxin secreted by Salmonella type Ⅰ virulence island (SPⅠ-1) in case 2 were two and one more than those in case 1, respectively. Some important virulence factors were predicted in the genome sequences of both strains, including type Ⅵ secretion system (T6SS), protease (IcsP/SopA), temperature-sensitive hemagglutinin (Tsh), non-LEE encoding T3SS effector (NleC), and Iron uptake protein(iucA、iutA). The two strains identified in this study are clones of the same serotype, sequence type, and T6SS, but exhibit different antibiotic resistance profiles, and there is no history of common exposure among the infants with diarrhea. This suggests that S.Ⅲb 50:z₅₂:z₃₅/ST8433 clone possesses high recombination and virulence characteristics.