Mutation of smeRv Renders Stenotrophomonas maltophilia Resistant to First-Line Antibiotics Trimethoprim/Sulfamethoxazole and Levofloxacin

<b>Background:</b><i>Stenotrophomonas maltophilia</i> is one of the common causative agents of hospital-acquired infections worldwide. The major concern regarding <i>S. maltophilia</i> infections is its extreme resistance to multiple antibiotics. <b>Methods:</b> Enrofloxacin-resistant mutants of <i>S. maltophilia</i> K279a were selected using a serial passage technique. <b>Results:</b> In this study, we showed that one of the mutant strains, KE507, which was selected from <i>S. maltophilia</i> K279a for its resistance to the veterinary drug enrofloxacin, conferred resistance to trimethoprim/sulfamethoxazole (co-trimoxazole), levofloxacin, and minocycline as per the Clinical and Laboratory Standards Institute guideline. These antibiotics are the first-line drugs routinely used to treat <i>S. maltophilia</i> infections. The KE507 mutant also showed increased resistance to all tested quinolones, azithromycin, and neomycin. Molecular characterization using whole genome sequencing, antibiotic resistance gene expression profiles, and mutational analysis indicated that inactivation of SmeRv (Q208insHSPRFTW), a transcriptional regulator of the SmeVWX multidrug efflux pump, contributes to resistance to quinolones (including levofloxacin), co-trimoxazole, and partially to neomycin, but not to azithromycin or minocycline. These data, together with in silico structural analysis, suggest that the mutation of SmeRv causes a conformational change in the SmeRv structure, which leads to the activation of SmeVWX efflux transporter expression and subsequent resistance to co-trimoxazole and quinolone antibiotics. <b>Conclusion:</b><i>S. maltophilia</i> can thus acquire resistance to the antibiotics primarily used to treat <i>S. maltophilia</i> infections through the mutation of SmeRv.