Advances in the Microbiology of Stenotrophomonas maltophilia

Abstract

Stenotrophomonas maltophilia is an opportunistic pathogen of significant concern to susceptible patient populations. This pathogen can cause nosocomial and community-acquired respiratory and bloodstream infections and various other infections in humans. Sources include water, plant rhizospheres, animals, and foods. Studies of the genetic heterogeneity of S. maltophilia strains have identified several new genogroups and suggested adaptation of this pathogen to its habitats. The mechanisms used by S. maltophilia during pathogenesis continue to be uncovered and explored. S. maltophilia virulence factors include use of motility, biofilm formation, iron acquisition mechanisms, outer membrane components, protein secretion systems, extracellular enzymes, and antimicrobial resistance mechanisms. S. maltophilia is intrinsically drug resistant to an array of different antibiotics and uses a broad arsenal to protect itself against antimicrobials. Surveillance studies have recorded increases in drug resistance for S. maltophilia, prompting new strategies to be developed against this opportunist. The interactions of this environmental bacterium with other microorganisms are being elucidated. S. maltophilia and its products have applications in biotechnology, including agriculture, biocontrol, and bioremediation.

Keywords: S. maltophilia; Stenotrophomonas; antimicrobial agents; antimicrobial resistance; biofilms; biotechnology; cystic fibrosis; genomes; pathogenesis; risk factors.

FIG 1

Properties of S. maltophilia. For clarity of viewing, not all properties are shown. Not drawn to scale.

FIG 2

Effect of WT and Xps mutant supernatant on various human and murine cell lines. (A) The A549, HeLa, MLE, and 3T3 cell lines were incubated for 3 h with 25% (vol/vol) supernatants from strain K279a (WT), the xpsF mutant NUS4 (xpsF), the complemented xpsF mutant (xpsF/pxpsF), or a medium control. Mammalian cell morphology was evaluated by phase-contrast light microscopy. Data are representative of three independent experiments. (B) Cell lines were incubated with WT supernatant at the indicated doses for 3 h and washed, and then the remaining adherent cells were quantified by measuring absorbance at OD₆₀₀. Data were normalized to the value for cells treated with medium alone, which was set at 100% adherence. An asterisk indicates a statistically significant difference from A549 and HeLa cells (P < 0.05). (C) Cell lines were incubated for 3 h with 25% (vol/vol) supernatants from the WT, the mutant, and the complemented mutant. Cell detachment was determined as described for panel B. Single and double asterisks indicate statistically significant differences from the WT and the xpsF strain, respectively (P < 0.05). For panels B and C, data are means and standard errors of the means (SEM) from three independent experiments. (Figure reproduced and legend adapted from reference with permission.) OD₆₀₀, optical density at 600 nm.

FIG 3

S. maltophilia and P. aeruginosa stratify within polymicrobial biofilms in vitro. Structural composition of polymicrobial biofilms was assessed via confocal imaging of S. maltophilia K279a (GFP+), P. aeruginosa mPA0831 (mCherry+), or both grown at 30°C for 8 h. Single-species biofilms of S. maltophilia K279a (GFP+) (A) and P. aeruginosa mPA0831 (mCherry+) (B) were imaged at ×40 magnification. Dual-species foci were imaged at ×40 magnification (C) and zoomed 4× for a total magnification of ×160 (D). (Figure reproduced and legend adapted from reference with permission.)

FIG 4

(A) T-seeded colony-based DSF bioassay of strains E77 and M30. Arrow indicates DSF production of M30 (rpf-2) strain upon detection of DSF molecules produced by E77 (rpf-1). (B) DSF quantification of supernatants from axenic cultures of E77 and M30, a mixed culture E77:M30 (1:1), an axenic culture of M30 supplemented with synthetic DSF at 0.05 μM final concentration and a corresponding control (equal volume of LB broth containing 0.05 μM DSF), using the microtiter DSF bioassay; *, P < 0.05 by one-way ANOVA and posttest. (C) Colony-based DSF bioassay of E77, M30 and their respective ΔrpfF mutants seeded at different distances on the same agar plate. (Figure reproduced and legend adapted from reference with permission.) ANOVA, analysis of variance.