Role of Enterococcus faecalis surface protein Esp in the pathogenesis of ascending urinary tract infection

Abstract

Enterococcus faecalis bacteria isolated from patients with bacteremia, endocarditis, and urinary tract infections more frequently express the surface protein Esp than do fecal isolates. To assess the role of Esp in colonization and persistence of E. faecalis in an animal model of ascending urinary tract infection, we compared an Esp(+) strain of E. faecalis to its isogenic Esp-deficient mutant. Groups of CBA/J mice were challenged transurethrally with 10(8) CFU of either the parent or mutant strain, and bacteria in the urine, bladder, and kidneys were enumerated 5 days postinfection. Significantly higher numbers of bacteria were recovered from the bladder and urine of mice challenged with the parent strain than from the bladder and urine of mice challenged with the mutant. Colonization of the kidney, however, was not significantly different between the parent and mutant strains. Histopathological evaluations of kidney and bladder tissue done at 5 days postinfection did not show marked histopathological changes consistent with inflammation, mucosal hyperplasia, or apoptosis, and there was no observable difference between the mice challenged with the parent and those challenged with the mutant. We conclude that, while Esp does not influence histopathological changes associated with acute urinary tract infections, it contributes to colonization and persistence of E. faecalis at this site.

FIG. 1

Schematic of the strategy used to create an Esp-deficient mutant. Gray arrows within pNS110 denote the directions of transcription for these determinants. Black arrows adjacent to the esp gene on the MMH594 chromosome indicate the positions of primers used to verify proper integration in the single-crossover and double-crossover mutants.

FIG. 2

Ethidium bromide-stained agarose gel electrophoresis of PCR-amplified products from parent (MMH594), single-crossover integrant (SCO), and double-crossover integrant (DCO; MMH594b). Molecular size markers are shown in lane M.

FIG. 3

Back scatter electron imaging of colloidal gold-immunolabeled Esp protein. (A) Representative view of the isogenic mutant strain (MMH594b) which exhibits no binding of colloidal gold to the cell surface. (B) Typical view of the parent strain MMH594.

FIG. 4

In vitro growth characteristics of the parent and isogenic mutant strains in brain heart infusion broth. Data points along the growth curve represent the means of three independent measurements from bacteria grown without antibiotic selection. Growth characteristics of parent and mutant strains grown in the presence of antibiotics were identical and superimposable.

FIG. 5

Distribution of CFU quantified from urine, bladder, and kidneys of mice challenged with parent or Esp-deficient E. faecalis. Data are expressed as log₁₀ CFU per milliliter of urine or per gram of bladder or kidney homogenates 5 days after transurethral challenge (n = 20). The mean (*) is indicated for each group.