Abstract
Plesiomonas shigelloides, a Gram-negative bacterium prevalent in aquatic environments and also frequently isolated from livestock and poultry, was investigated through integrated whole-genome sequencing and functional analyses. We deciphered the pathogenic mechanisms of P. shigelloides CA-HZ1, a highly virulent strain isolated from a novel piscine host, revealing a complete genome assembly with a 3.49 Mb circular chromosome and 311 kb plasmid housing 3247 predicted protein-encoding genes. Critical genomic features included 496 virulence factors and 225 antibiotic resistance genes. Pathogenicity analysis indicated that P. shigelloides was responsible for disease outbreaks. Antimicrobial susceptibility tests showed resistance to various drugs, such as kanamycin, erythromycin, and penicillin. Histopathological examination showed significant alterations in the infected hosts. Quantitative real-time PCR (qRT-PCR) was carried out to analyze immune-related gene (IL-6, IL-1β, IL-21, STAT1, and HSP70) levels in liver and intestinal tissues, demonstrating the potent immunity triggered by P. shigelloides infection. An analysis of the liver transcriptome revealed that P. shigelloides has the potential to influence the cellular composition, molecular functions, and biological processes. Collectively, this study describes the genomic basis underlying both the pathogenic potential and hypervirulence of P. shigelloides CA-HZ1, establishing a foundational framework for investigating its broad host tropism and immune response.