A Linkage between SmeIJK Efflux Pump, Cell Envelope Integrity, and σE-Mediated Envelope Stress Response in Stenotrophomonas maltophilia

Abstract

Resistance nodulation division (RND) efflux pumps, such as the SmeIJK pump of Stenotrophomonas maltophilia, are known to contribute to the multidrug resistance in Gram-negative bacteria. However, some RND pumps are constitutively expressed even though no antimicrobial stresses occur, implying that there should be some physical implications for these RND pumps. In this study, the role of SmeIJK in antimicrobials resistance, envelope integrity, and σE-mediated envelope stress response (ESR) of S. maltophilia was assessed. SmeIJK was involved in the intrinsic resistance of S. maltophilia KJ to aminoglycosides and leucomycin. Compared with the wild-type KJ, the smeIJK deletion mutant exhibited growth retardation in the MH medium, an increased sensitivity to membrane-damaging agents (MDAs), as well as activation of an σE-mediated ESR. Moreover, the expression of smeIJK was further induced by sub-lethal concentrations of MDAs or surfactants in an σE-dependent manner. These data collectively suggested an alternative physiological role of smeIJK in cell envelope integrity maintenance and σE-mediated ESR beyond the efflux of antibiotics. Because of the necessity of the physiological role of SmeIJK in protecting S. maltophilia from the envelope stress, smeIJK is constitutively expressed, which, in turn, contributes the intrinsic resistance to aminoglycoside and leucomycin. This is the first demonstration of the linkage among RND-type efflux pump, cell envelope integrity, and σE-mediated ESR in S. maltophilia.

Vitamin K 3 Induces the Expression of the Stenotrophomonas maltophilia SmeVWX Multidrug Efflux Pump

“…Different compounds from different categories were used in this assay at serial concentrations. Among them were the antibiotics erythromycin (512, 256, and 128 g/ml), gentamicin (32,16, and 8 g/ml), co-trimoxazole (trimethoprimsulfamethoxazole, 1:5) (1, 0.5, and 0.25 g/ml), chloramphenicol (16,8, and 4 g/ml), tobramycin (512, 256, and 128 g/ml), ofloxacin (4, 2, and 1 g/ml), kanamycin (512, 256, and 128 g/ml), tetracycline (4, 2, and 1 g/ml), polymyxin B (2, 1, and 0.5 g/ml), and colistin (24, 12, and 6 g/ml); heavy metals ZnSO 4 (5, 2.5, and 1.25 mM), CuSO 4 (5, 2.5, and 1.25 mM), CdSO 4 (5, 2.5, and 1.25 mM), CoSO 4 (5, 2.5, and 1.25 mM), and FeCl 3 (5, 2.5, and 1.25 mM); oxidative stress compounds paraquat (5, 2.5, and 1.25 mM), vitamin K 3 (2, 1, and 0.5 mM), and tert-butyl hydroperoxide (1, 0.5, and 0.25 mM); biocides triclosan (10, 5, and 2.5 g/ml) and hexachlorophene (100, 50, and 25 g/ml); plant-produced flavonoids phloretin (10, 5, and 2.5 g/ml), quercetin (10, 5, and 2.5 g/ml), and genistein (10, 5, and 2.5 g/ml); detergents SDS (200, 100, and 50 mM) and Tween 20 (200, 100, and 50 mM); chelating agents EDTA (2, 1, and 0.5 mM) and EGTA (2, 1, and 0.5 mM); the analgesic metamizol (10, 5, and 2.5 mg/ml); and the inhibitor of oxidative phosphorylation carbonyl cyanide m-chlorophenyl hydrazone (CCCP; 20, 10, and 5 M). The compounds vitamin K 3 , vitamin K 2 , plumbagin, and tert-butyl hydroperoxide were studied in more detail using a wider range of concentrations.…”

“…The roles of six of them (SmeABC, SmeDEF, SmeIJK, SmeOP, SmeVWX, and SmeYZ) in intrinsic and acquired resistance to antibiotics have been analyzed (5)(6)(7)(8)(9)(10)(11)(12)(13)(14).…”

The Challenge of Efflux-Mediated Antibiotic Resistance in Gram-Negative Bacteria

“…Reactive oxygen species-mediated killing in macrophages is alleviated by MacAB (907). Both SmeIJK and MacABC of S. maltophilia also contribute to tolerance to oxidative and envelope stresses (582,584). In addition to the role of efflux pumps themselves in the stress response, the levels of several pump or OM protein regulators (e.g., MarA, SoxS, Rob, OmpR, and EnvZ) were elevated in the presence of antibiotic or chemical stress (908).…”

Overexpression of SmeDEF Efflux Pump Decreases Aminoglycoside Resistance in Stenotrophomonas maltophilia

“…The resistance to AGs reported in S. maltophilia is attributable to aminoglycoside-modifying enzymes (AMEs), RND-type efflux pumps, and outer membrane permeability (8,13,(14)(15)(16). Given that SmeT acts as a transcriptional repressor, we wondered whether SmeT also regulates the expression of AMEs, RND-type efflux pumps, and lytic transglycosidase genes, in addition to the smeDEF operon.…”