The osmotic stress response and virulence in pyelonephritis isolates of Escherichia coli: contributions of RpoS, Prop, ProU and other systems

Trehalose synthesis (RpoS-dependent) and betaine uptake mediated by transpo rters ProP and ProU contribute to the osmotolerance of Escherichia coli K-1 2. Pyelonephritis isolates CFT073 and HU734 were similar and diminished in osmotolerance, respectively, compared to E. coli K-12. The roles of RpoS, P roP and ProU in osmoregulation and urovirulence were assessed for these iso lates. Strain HU734 expressed an RpoS variant which had low activity and a C-terminal extension. This bacterium accumulated very little trehalose and had poor stationary-phase thermotolerance. For E. coli CFT073, introduction of an rpoS deletion impaired trehalose accumulation, osmotolerance and sta tionary-phase thermotolerance. The rpoS defects accounted for the differenc e in osmotolerance between these strains in minimal medium of very high osm olality (1.4 mol kg(-1)) but not in medium of lower osmolality (0.4 mol kg( -1)). The slow growth of both pyelonephritis isolates in high-osmolality me dium was stimulated by glycine betaine (GB) and deletion of proP and/or pro U impaired GB uptake. An HU734 derivative lacking both proP and proU retain ed osmoprotective GB uptake activity that could be attributed to system Bet U, which is not present in strain K-12 or CFT073. BetU transported GB (K-m, 22 muM) and proline betaine. High-osmolality human urine (0.92 mol kg(-1)) included membrane-permeant osmolyte urea (0.44 M) plus other constituents which contributed an osmolality of only approximately 0.4 mol kg(-1). Strai ns HU734 and CFT073 showed correspondingly low CB uptake activities after c ultivation in this urine. Deletion of proP and proU slowed the growth of E. coli HU734 in this high-osmolality human urine (which contains betaines) b ut had little impact on its colonization of the murine urinary tract after transurethral inoculation. By contrast, deletion of rpoS, proP and proU had no effect on the very rapid growth of CFT073 in high-osmolality urine or o n its experimental colonization of the murine urinary tract. RpoS-dependent gene expression is not essential for growth in human urine or colonization of the murine urinary tract. Additional osmoregulatory systems, some not p resent in E. coli K-12 (e.g. BetU), may facilitate growth of pyelonephritis isolates in human urine and colonization of mammalian urinary tracts. The contributions of systems prop and ProU to urinary tract colonization cannot be definitively assessed until all such systems are identified.