Occurrence of Stenotrophomonas carrying β-lactamase-encoding genes in a veterinary hospital environment

Stenotrophomonas spp. are environmental bacteria increasingly recognized as opportunistic pathogens with multidrug resistance. This study characterized 17 environmental Stenotrophomonas isolates recovered from effluent samples and veterinary hospitalization units. The species identified included S. maltophilia, S. hibiscicola, S. muris, and S. forensis, with 13 distinct sequence types (STs) detected, including ST1402, which was shared between both environments. Antimicrobial susceptibility testing revealed a high resistance profile to ciprofloxacin, whereas resistance to tetracyclines, chloramphenicol, levofloxacin, and trimethoprim/sulfamethoxazole was less frequent. In accordance with the reported intrinsic resistance of Stenotrophomonas to a range of antibiotic classes, the strains were resistant to meropenem, ampicillin, cefoxitin, and amoxicillin/clavulanate. Whole-genome sequencing confirmed the universal presence of intrinsic β-lactamase genes blaL1 and blaL2, indicating the genetic potential for β-lactamases production, as well as the widespread distribution of RND-type efflux pumps, including components of the SmeABC and SmeDEF systems. In addition, all isolates were strong biofilm formers. Together, these findings indicate that environmental Stenotrophomonas spp. strains from veterinary settings harbor multidrug resistance determinants, efflux-mediated mechanisms, and biofilm-forming capacity, highlighting their potential role in the maintenance and dissemination of clinically relevant antimicrobial resistance.