<i>Peribacillus suis</i> sp. nov. Isolated From the Pig Louse <i>Haematopinus suis</i> Reveals Unexpected Pathogenic Potential in a Traditionally Benign Genus

The pig sucking louse Haematopinus suis is a major swine ectoparasite and vector of pathogens, yet its microbiome remains understudied. Here, we described the isolation of a previously unrecognized bacterial strain, P8‐9 T , from the intestinal tract of H. suis . A comprehensive polyphasic analysis, including phenotypic characterization, phylogenomics, and whole‐genome comparisons, placed this isolate within Peribacillus . Genome‐based metrics confirmed its novelty, with average nucleotide identity and digital DNA–DNA hybridization values (&lt;80% and &lt;27%, respectively) falling far below accepted species delineation thresholds. We, therefore, proposed the designation Peribacillus suis sp. nov. Unexpectedly, the genome of P8‐9 T encodes an extensive repertoire of 219 putative virulence‐associated and antibiotic resistance genes; features atypical for a largely composed of environmental species considered saprophytic or beneficial. In vivo experiments revealed this pathogenic potential: intraperitoneal inoculation in mice resulted in all animals reaching predefined humane endpoints within 24 h, characterized by septicemia and widespread organ pathology, while oral exposure elicited splenomegaly, intestinal pathology, and a robust pro‐inflammatory response. This work represents the first report of a Peribacillus species isolated from an ectoparasite and provides direct experimental evidence of virulence within a genus traditionally viewed as benign.