The resistome and mobilome of multidrug-resistant Staphylococcus sciuri C2865 unveil a transferable trimethoprim resistance gene, designated dfrE, 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 (dfr). 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 dfrE, which confers high-level TMP resistance in Staphylococcus aureus and Escherichia coli. dfrE was located in a novel multidrug resistance mosaic plasmid (pUR2865-34) encompassing adaptive, mobilization, and segregational stability traits. dfrE was formerly denoted as dfr_like in Exiguobacterium spp. from fish farm sediment in China but escaped identification in one macrococcal and diverse staphylococcal genomes in different Asian countries. dfrE shares the highest identity with dfr of soil-related Paenibacillus anaericanus (68%). Data analysis discloses that dfrE 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-SCCmec cassette, three apparently functional prophages (Siphoviridae), and an SaPI4-related staphylococcal pathogenicity island. Since dfrE 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