Foodborne diarrhea outbreaks linked to Citrobacter species in East China 2022-2023.

The Citrobacter genus has emerged as an opportunistic pathogen in foodborne diarrhea outbreaks, as evidenced by two incidents in East China between 2022 and 2023. This study investigated the role of Citrobacter portucalensis and Citrobacter freundii in these outbreaks through a combination of epidemiological, metagenomic, and bioinformatic analyses. Our findings highlighted that C. portucalensis from the diarrhea outbreak harbored unique blaCMY-39 resistance genes and exhibited a distinct profile of virulence genes associated with motility, characterized by the absence of flagellar export chaperone genes fliE, fliQ, fliR, and the molecular chaperone gene clpB, along with the acquisition of the fliS gene. Antimicrobial susceptibility test revealed that one C. portucalensis strain resistant to ampicillin. Subsequent histological analysis showed that the diarrhea group had intestinal submucosal edema, with inflammation observed in the duodenum, ileum, and colon of infected mice. In general, this study underscores the importance of monitoring Citrobacter species in the context of food safety and emphasizes the neglected emerging pathogens implicated in these outbreaks in the region.