GROWTH TEMPERATURE-DEPENDENT VARIATION OF CELL-ENVELOPE LIPIDS AND ANTIBIOTIC SUSCEPTIBILITY IN STENOTROPHOMONAS (XANTHOMONAS) MALTOPHILIA

Clinical isolates of Stenotrophomanas (Xanthomonas) maltophilia showed growth temperature-dependent variation in susceptibility (TDVS) to aminoglycoside antibiotics between 30 degrees C and 37 degrees C, but little or no TDVS effect for polymixin B, colistin, ceftazidime, chloramphenicol and piperacillin. When phenylethanol was added at sub-inhibitory concentrations, the TDVS effect was eliminated. Gas liquid chromatography showed that 13-methyl tetradecanoate (i-15;0), was the predominant fatty acid, and was present in lower proportions in cells grown at 30 degrees C than 37 degrees C, by contrast to the unsaturated acids, which were found in increased proportions in cells grown at 30 degrees C. However, the extent of these shifts in composition did not correlate with the extent of the TDVS effect in individual strains. Membrane analysis by spin label-electron spin resonance spectroscopy showed that strains exhibiting TDVS had significantly decreased membrane fluidity compared with susceptible strains at 30 degrees C. Furthermore, analysis of the outer and cytoplasmic membranes from the strains with TDVS revealed that in organisms grown at 30 degrees C, the outer membrane remained in a more rigid conformation than the cytoplasmic membrane. We conclude that resistance of S. maltophilia to aminoglycoside antibiotics at 30 degrees C correlates with changes in the conformation of the outer membrane so that binding and/or uptake of the antibiotic is inhibited.