Enterococcus faecalis was tested for the ability to persist in mouse peritoneal macrophages in two separate studies. In the first study, the intracellular survival of serum-passaged E. faecalis 418 and two isogenic mutants [cytolytic strain FA2-2(pAM714) and non-cytolytic strain FA2-2(pAM771)] was compared with that of Escherichia coli DH5α by infecting BALB/c mice intraperitoneally and then monitoring the survival of the bacteria within lavaged peritoneal macrophages over a 72-h period. All E. faecalis isolates were serum passaged to enhance the production of cytolysin. E. faecalis 418, FA2-2(pAM714), and FA2-2(pAM771) survived at a significantly higher level (P = 0.0001) than did E. coli DH5α at 24, 48, and 72 h. Internalized E. faecalis 418, FA2-2(pAM714), and FA2-2(pAM771) decreased 10-, 55-, and 31-fold, respectively, over the 72-h infection period, while internalizedE. coli DH5α decreased 20,542-fold. The difference in the rate of survival of E. faecalis strains and E. coli DH5α was most prominent between 6 and 48 h postinfection (P = 0.0001); however, no significant difference in killing was observed between 48 and 72 h postinfection. In the second study, additional E. faecalisstrains from clinical sources, including DS16C2, MGH-2, OG1X, and the cytolytic strain FA2-2(pAM714), were compared with the nonpathogenic gram-positive bacterium, Lactococcus lactis K1, for the ability to survive in mouse peritoneal macrophages. In these experiments, the E. faecalis strains and L. lactis K1 were grown in brain heart infusion (BHI) broth to ensure that there were equal quantities of injected bacteria. E. faecalis FA2-2(pAM714), DS16C2, MGH-2, and OG1X survived significantly better (P < 0.0001) than did L. lactis K1 at each time point. L. lactis K1 was rapidly destroyed by the macrophages, and by 24 h postinfection, viable L. lactis could not be recovered. E. faecalis FA2-2(pAM714), DS16C2, MGH-2, and OG1X declined at an equivalent rate over the 72-h infection period, and there was no significant difference in survival or rate of decline among the strains. E. faecalis FA2-2(pAM714), MGH-2, DS16C2, and OG1X exhibited an overall decrease of 25-, 55-, 186-, and 129-fold respectively, between 6 and 72 h postinfection. The overall reduction by 1.3 to 2.27 log units is slightly higher than that seen for serum-passaged E. faecalis strains and may be attributable to the higher level of uptake of serum-passaged E. faecalis than of E. faecalis grown in BHI broth. Electron microscopy of infected macrophages revealed that E. faecalis 418 was present within an intact phagocytic vacuole at 6 h postinfection but that by 24 h the infected macrophages were disorganized, the vacuolar membrane was degraded, and the bacterial cells had entered the cytoplasm. Macrophage destruction occurred by 48 h, and the bacteria were released. In conclusion, the results of these experiments indicate that E. faecaliscan persist for an extended period in mouse peritoneal macrophages.

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...

Prostaglandins of the E series inhibit the development of Th1 responses. When infected with Leishmania major, BALB/c mice fail to develop a Th1 response, but instead mount a Th2 response and die of the disease. Therefore, we treated L. major-infected BALB/c mice with indomethacin, which inhibits prostaglandin production. Indomethacin lessened disease severity (parasite burden and pathology), and promoted a Th1 response, but the mice still succumbed to infection. The explanation for these observations may be two-fold: (1) the beneficial effects of indomethacin were predominantly observed later in infection (beyond two weeks), a time at which indomethacin was unable to sufficiently block the development of a Th2 response; (2) indomethacin was unable to induce a Th1 response in BALB/c mice that was of the same magnitude as the Th1 response observed in C57BL/6 mice infected with L. major.