The Resistome and Mobilome of Multidrug-Resistant Staphylococcus sciuri C2865 Unveil a Transferable Trimethoprim Resistance Gene, Designated , Spread Unnoticed.

Methicillin-resistant Staphylococcus sciuri (MRSS) strain C2865 from a stranded dog in Nigeria was trimethoprim (TMP) resistant but lacked formerly described staphylococcal TMP-resistant dihydrofolate reductase genes (). Whole-genome sequencing, comparative genomics, and pan-genome analyses were pursued to unveil the molecular bases for TMP resistance via resistome and mobilome profiling. MRSS C2865 comprised a species subcluster and positioned just above the intraspecies boundary. Lack of species host tropism was observed. S. sciuri exhibited an open pan-genome, while MRSS C2865 harbored the highest number of unique genes (75% associated with mobilome). Within this fraction, we discovered a transferable TMP resistance gene, named , which confers high-level TMP resistance in Staphylococcus aureus and Escherichia coli. was located in a novel multidrug resistance mosaic plasmid (pUR2865-34) encompassing adaptive, mobilization, and segregational stability traits. was formerly denoted as in spp. from fish farm sediment in China but escaped identification in one macrococcal and diverse staphylococcal genomes in different Asian countries. shares the highest identity with of soil-related Paenibacillus anaericanus (68%). Data analysis discloses that has emerged from a single ancestor and places S. sciuri as a plausible donor. C2865 unique fraction additionally enclosed novel chromosomal mobile islands, including a multidrug-resistant pseudo-SCC cassette, three apparently functional prophages (), and an SaPI4-related staphylococcal pathogenicity island. Since seems not yet common in staphylococcal clinical specimens, our data promote early surveillance and enable molecular diagnosis. We evidence the genome plasticity of S. sciuri and highlight its role as a resourceful reservoir for adaptive traits. The discovery and surveillance of antimicrobial resistance genes (AMRG) and their mobilization platforms are critical to understand the evolution of bacterial resistance and to restrain further expansion. Limited genomic data are available on Staphylococcus sciuri; regardless, it is considered a reservoir for critical AMRG and mobile elements. We uncover a transferable staphylococcal TMP resistance gene, named , in a novel mosaic plasmid harboring additional resistance, adaptive, and self-stabilization features. is present but evaded detection in diverse species from varied sources geographically distant. Our analyses evidence that the -carrying element has emerged from a single ancestor and position S. sciuri as the donor species for spread. We also identify novel mobilizable chromosomal islands encompassing AMRG and three unrelated prophages. We prove high intraspecies heterogenicity and genome plasticity for S. sciuri. This work highlights the importance of genome-wide ecological studies to facilitate identification, characterization, and evolution routes of bacteria adaptive features.