Investigation and pathogenetic testing of Shewanella spp. positive diarrhea cases in Beijing, China

The pathogenic profiles of seven Shewanella spp. positive cases identified during diarrhea surveillance in Beijing, China, in 2023 were characterised. Sentinel hospitals collected patient information and stool samples, while regional centres for disease control (CDC) performed cultures and real time PCR. Whole-genome sequencing (WGS), average nucleotide identity (ANI) analysis, phylogenetic analysis, virulence gene and resistance gene analysis of the Shewanella spp. isolates were conducted, as well as phenotypic resistance analysis. The detection rate in the stool samples collected from 354 diarrhea patients was 1.98% (7/354). The time of disease onset of six out of the seven patients ranged from July 17-22, 2023. The incubation period ranged from 8 to 12 h with 3-50 episodes/day. Three subjects reported having consumed potentially contaminated seafood. The seven isolated strains of Shewanella spp. (named as S1-S7) were closely related to S. algae, belonged to the algae clade, and were all novel ST (sequence typing) strains. A total of 125,738 SNPs (single nucleotide polymorphism) were identified in the core genomes of the seven Shewanella strains. Twenty-six virulence-related genes in five categories were identified, with chemotaxis and flagella-related genes being the most abundant (26.92%, 7/26), followed by secretion system- and serum resistance-related genes at 23.08% (6/26) and 15.38% (4/26), respectively. Shewanella spp. were detected in patients with diarrhea at a certain level. Seafood should be the key food category for monitoring and seafood markets should become a key monitoring site for Shewanella spp. The novel STs of the algae clade isolated from diarrhea patients in this study may potentially help in tracking circulating strains. Further in-depth investigations are required to precisely elucidate the correlation between Shewanella infections and human diarrhea and the pathogenic characteristics of this infection.