The Efflux Pump SmeDEF Contributes to Trimethoprim- Sulfamethoxazole Resistance in Stenotrophomonas maltophilia

Trimethoprim-sulfamethoxazole (co-trimoxazole) is one of the antimicrobials of choice for the treatment of Stenotrophomonas maltophilia infections. The analysis of mutants either lacking or overexpressing the efflux pump SmeDEF shows that this efflux pump contributes to intrinsic and acquired co-trimoxazole resistance in S. maltophilia. Since SmeDEF can extrude a variety of antibiotics, selection with such antimicrobials, including quinolones, might also select for S. maltophilia co-trimoxazole resistance. The treatment of Stenotrophomonasmaltophilia, an opportunis-tic pathogen involved in different nosocomial infections, is difficult, owing to its low level of susceptibility to several antibiot-ics and its capability to acquire further resistance during clinical treatment. The intrinsic resistance of this pathogen is mainly due to the presence in its genome of genes encoding different resis-tance determinants, as several multidrug resistance (MDR) efflux pumps and antibiotic-modifying enzymes, and the quinolone re-sistance gene Smqnr (1, 2). Acquired resistance is mediated by the acquisition ofmobile genetic elements containing antibiotic resis-tance genes and by the overexpression of chromosomal resistanc