Distinct phenotypic and genetic features of Stenotrophomonas maltophilia complex from the oral cavity compared with those of blood-derived strains

Antimicrobial-resistant (AMR) bacteria are a global threat, and elucidating their epidemiological dynamics and colonization and transmission mechanisms is urgently needed. Stenotrophomonas maltophilia complex possesses intrinsic multidrug resistance and is associated with high-mortality infections, particularly in immunocompromised patients. In recent years, it has also been suggested that oral bacteria may serve as reservoirs for systemic infections; however, the specific phenotypes and genetic backgrounds of the S. maltophilia complex in the oral cavity remain unclear. In this study, the phenotypic and genomic characteristics of oral S. maltophilia complex isolates were compared with those of isolates derived from blood to clarify differences in adaptation strategies and pathogenicity based on the source. Fifty isolates (30 oral-derived, 20 blood-derived) were studied for genomic and phenotypic analysis. The oral S. maltophilia complex included seven species, including S. maltophilia (43.3%), while the blood S. maltophilia complex included five species, including S. maltophilia (40.0%). In particular, S. geniculate (20.0%) and S. pavanii (15.0%) were only isolated from the oral cavity and blood, respectively. Whole-genome comparative analysis showed no clear source-specific separation between oral- and blood-derived isolates based on core-genome phylogeny or accessory-gene presence/absence patterns. Phenotypic analyses revealed no significant differences in antimicrobial susceptibility, biofilm formation or zeta-potential among bacterial species. However, oral-derived strains had stronger growth ability, greater self-aggregation, aggregation with artificial saliva and coaggregation with S. mutans , greater swimming/swarming motility. Phylogenetic signal testing indicated that growth ability, biofilm formation and self-aggregation were constrained by core genome phylogeny. Electron microscopic observation confirmed the flagella of the isolates with high motility. These findings indicate that oral strains retain the genetic and phenotypic potential to cause opportunistic infection during immunosuppression, underscoring our understanding of their adaptation.