Intravenous Mouse Infection Model for Studying the Pathology ofEnterococcus faecalisInfections

Abstract

An intravenous mouse infection model was used to compare the virulence of Enterococcus faecalis strains, to study bacterial localization and organ histopathology, and to examine the effects of Nramp1 and gamma interferon (IFN-␥) on the course of infection. Infection of BALB/c mice with 5 ؋ 10 8 CFU of E. faecalis JH2-2, MGH-2, 418, DS16C2, or OG1X revealed the following virulence ranking (from highest to lowest): MGH-2, 418, DS16C2, JH2-2, and OG1X. Discernible differences in the number of MGH-2 and JH2-2 bacteria were observed at 7 days (168 h) in the blood (P ‫؍‬ 0.037), at 72 h in the liver (P ‫؍‬ 0.002), and at 8 h in the spleen (P ‫؍‬ 0.036). At these time points, the number of MGH-2 bacteria was higher in the blood and liver while the number of JH2-2 bacteria was higher in the spleen. At 72 h, livers from MGH-2-infected mice had higher numbers of coalescing aggregates of leukocytes and a greater degree of caseous necrosis than those from JH2-2-infected mice. These results indicate a correlation between the virulence of the E. faecalis strain, the number of bacteria in the liver, and the degree of histopathology of the liver at 72 h postinfection. IFN-␥ was important in E. faecalis infection, since IFN-␥ gene knockout mice had reduced mortality and massive coagulative necrosis was observed in wild-type mice. The contribution of Nramp1 was unclear, since Nramp1 ؊/؊ mice and the respective control mice were innately resistant to E. faecalis. The mortality of mice in this model is probably due to induction of cytokine release and massive coagulative necrosis.Enterococcus faecalis is the third leading nosocomial isolate from patients with bacteremia (11). Bacteremia with E. faecalis is a life-threatening condition that causes death in 28 to 75% of patients (1,14,17,29,31,37,44,53) and has a mortality rate of 1.7 to 20% in patients who develop endocarditis (3,14,32,37,52,53). Bloodstream infections with E. faecalis can occur due to contamination of intravenous catheters, ascending urinary tract infections following catheterization, intravenous drug abuse, or abdominal surgery (2,4,12,17,25,26,31,33). Many studies have focused on demonstrating that the presence of specific virulence factors such as aggregation substance, cytolysin, surface protein EspA, and extracellular superoxide production are closely associated with E. faecalis isolates from bacteremic patients (20,21,30,42). Results from these studies suggest that the presence of these virulence factors (or a subset of these factors) may augment the ability of E. faecalis to exist in the bloodstream, since fecal isolates less frequently contain these factors.Animal studies to determine the role of virulence factors in disease (41,45,46) or to study antimicrobial efficacy (5, 6, 34-36) have often relied on intraperitoneal injection of mice with E. faecalis, either alone (23) or in conjunction with a virulence adjuvant such as mucin or sterile rat fecal extracts (5,35,46). Preliminary studies in our laboratory have shown that the use of the intraperitoneal inf...

Redox Balance via Lactate Dehydrogenase Is Important for Multiple Stress Resistance and Virulence in Enterococcus faecalis

“…Virulence experiments. To test the virulence of both JH2-2 and V583 ldh deletion mutants, we used an adaptation of a well-established intravenous infection model (19), as described by Michaux et al previously (20). Briefly, the strains were cultured overnight in BHI broth supplemented with 40% heat-inactivated horse serum; the cultures were centrifuged; and the resulting pellets were resuspended in sterile phosphate-buffered saline (PBS).…”

SlyA Is a Transcriptional Regulator Involved in the Virulence of Enterococcus faecalis

“…Larval killing was then monitored at 20 h postinfection. The virulences of V19 and the slyA deletion mutant were also assessed in an intravenous infection model, essentially as described by Gentry-Weeks et al (11). Briefly, overnight cultures of the strains grown in brain heart infusion broth (BHI) supplemented with 40% heat-inactivated horse serum were centrifuged, and the resulting pellets were resuspended in sterile phosphate-buffered saline (PBS) to achieve final concentrations of 1 ϫ 10 9 bacteria/ml.…”

Comparative Genomic Hybridization Analysis of Enterococcus faecalis : Identification of Genes Absent from Food Strains

“…E. faecalis causes 60 to 80% of enterococcal infections. Less than 2% of infections are due to strains resistant to clinically relevant antibiotics, ampicillin and vancomycin, implying that other genetic factors are necessary for E. faecalis infection and virulence potential (30).Phenotypic studies suggest that E. faecalis strains vary in their colonization and invasion abilities and, thus, likely vary in their virulence potential (14,26,39). Overall genetic diversity of E. faecalis has been reported using various molecular typing methods (for review, see reference 18; also J. C. Ogier and P. Serror, submitted for publication).…”