Abstract
Urinary tract infections are the most common cause of E. coli bloodstream infections (BSI) but the mechanism of bloodstream invasion is poorly understood. Some clinical isolates have been observed to shield themselves with extracellular amyloid fibers called curli at physiologic temperature. We hypothesize that curli fiber assembly at 37°C promotes bacteremic progression by urinary E. coli strains. Curli expression by cultured E. coli isolates from bacteriuric patients in the presence and absence of bacteremia were compared using Western blotting following amyloid fiber disruption with hexafluoroisopropanol. At 37°C, urinary isolates from bacteremic patients were more likely to express curli than those from non-bacteremic patients [16/22 (73%) vs. 7/21 (33%); p = 0.01]. No significant difference in curli expression was observed at 30°C [86% (19/22) vs. 76% (16/21); p = 0.5]. Isolates were clonally diverse between patients, indicating that this phenotype is distributed across multiple lineages. Most same-patient urine and blood isolates were highly related, consistent with direct invasion of urinary bacteria into the bloodstream. 37°C curli expression was associated with bacteremic progression of urinary E. coli isolates in this population. These findings suggest new future diagnostic and virulence-targeting therapeutic approaches.
Highlights
Curli fibers are extracellular amyloid fibrils that are variably expressed by E. coli
Patient Isolates To determine whether curli fiber expression is associated with urinary-source bacteremia, we compared bacterial isolates from 22 bacteremic patients to 21 non-bacteremic urinary isolate controls [19]
In this study of E. coli isolates, we observed a correlation between bacterial curli fiber expression at 37uC and secondary E. coli bloodstream infection
Summary
Curli fibers are extracellular amyloid fibrils that are variably expressed by E. coli (for review, see [1]). Curli fibers are deliberately assembled by dedicated bacterial machinery [3,4,5,6]. The curli fiber biogenesis requires both structural (CsgA and CsgB) and non-structural (CsgD, CsgE, CsgF, and CsgG) components encoded by genes on two divergent operons [4,5,7,8]. Curli fibers are composed of primarily CsgA proteins with CsgB proteins as minor components. CsgB monomers are exported outside of bacteria through CsgG pores, fold into proper conformation, and associate with bacterial cell surface [7]. Chaperoned by CsgE proteins, CsgA monomers are exported in the same fashion as unfolded proteins out to the cell surfaces
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