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PubMed1994

Enterococcus faecalis aggravates pyelonephritis caused by Pseudomonas aeruginosa in experimental ascending mixed urinary tract infection in mice.

Mixed urinary tract infection was caused by simultaneous inoculation of 10(4) CFU each of Enterococcus faecalis TN2005 and Pseudomonas aeruginosa P9 into the bladders of CBA/J mice. Both organisms proliferated in the kidneys, and viable cell counts of E. faecalis TN2005 reached a peak level of 4.1 x 10(5) CFU per pair of kidneys within the first 24 h, while P. aeruginosa P9 counts increased more slowly. The number of P. aeruginosa P9 cells peaked at 8.3 x 10(6) CFU per pair of kidneys 5 days after infection. Five days after mixed infection, infiltration of neutrophils into the renal pelvis and renal medulla was observed. Immunohistochemical staining revealed the presence of E. faecalis antigen in the renal medulla. P. aeruginosa antigen was detected mainly in the renal pelvis 5 days after infection and in the renal medulla as well as the renal pelvis 14 days after infection. Mixed infection induced pyelonephritis within 5 days after mixed infection, while it was not observed until 14 days after infection with P. aeruginosa P9 alone. P. aeruginosa P9 inoculated together with E. faecalis TN2005 was more resistant to eradication from the kidneys by beta-lactam antibiotics than P. aeruginosa P9 inoculated alone. These results suggest that E. faecalis TN2005 invades the renal medulla first in mixed urinary tract infection and induces histological changes which lead to aggravation of the pyelonephritis caused by P. aeruginosa P9.

Animals↗
PubMed1995

Molecular and structural requirements of a lipoteichoic acid from Enterococcus hirae ATCC 9790 for cytokine-inducing, antitumor, and antigenic activities.

Comparison was made between the immunobiological and antigenic properties of two lipoteichoic acid (LTA) fractions (LTA-1 and -2) from Enterococcus hirae ATCC 9790, their glycolipid portions, and synthetic compounds partially mimicking the above bacterial products. The more lipophilic LTA-2 fraction was capable of inducing serum tumor necrosis factor alpha and interleukin-6 in muramyldipeptide-primed mice and serum gamma interferon in those primed with Propionibacterium acnes. The LTA-2 fraction also induced tumor necrosis factor alpha, interleukin-6, and thymocyte-activating factor (essentially interleukin-1) in murine peritoneal macrophage cultures. Consecutive intravenous injections of muramyldipeptide and the LTA-2 fraction in Meth A fibrosarcoma-bearing BALB/c mice caused hemorrhagic necrosis and marked regression leading to complete regression of the tumor with no accompanying weakening or lethal effects. The LTA-2 fraction was at least 10,000-fold less pyrogenic in rabbits than a reference endotoxic lipopolysaccharide. The more hydrophilic LTA-1 fraction, on the other hand, showed at most marginal activity in the in vivo and in vitro assays. Natural glycolipids (NGL-1 and -2) which were prepared from a chloroform-methanol extract of Streptococcus pyogenes and E. hirae cells, and comparable in structure to the lipid moieties of the LTA-1 and -2 fractions, respectively, were practically inactive in all of the assays. None of the test synthetic compounds was immunobiologically active, although synthetic partial counterparts of the structure of LTA proposed by W. Fischer (Handb. Lipid Res. 6:123-234, 1990) reacted with murine monoclonal antibody TS-2, which was raised against OK-432, a penicillin-killed S. pyogenes preparation, and capable of neutralizing the cytokine-inducing activities of the LTA-2 fraction.

Acetylmuramyl-Alanyl-Isoglutamine↗
PubMed1995

Cloning of an Enterococcus faecalis endocarditis antigen: homology with adhesins from some oral streptococci.

Serum from a patient with Enterococcus faecalis endocarditis was used to identify the gene efaA cloned in Lambda ZapII in Escherichia coli. Nucleotide sequence analysis revealed a 924-bp open reading frame encoding a protein with a predicted molecular weight of 34,768. The amino acid sequence of EfaA shows 55 to 60% homology to a group of streptococcal proteins, FimA from Streptococcus parasanguis, SsaB from Streptococcus sanguis, ScaA from Streptococcus gordonii, and PsaA from Streptococcus pneumoniae. Members of this group have been shown to be adhesins, and we hypothesize that EfaA may function as an adhesin in endocarditis.

Adhesins, Bacterial↗
PubMed1997

Evidence of the proinflammatory role of Enterococcus faecalis in polymicrobial peritonitis in rats.

Although the role of members of the Enterobacteriaceae and anaerobes in the pathogenesis of intra-abdominal infections has been extensively demonstrated, the role played by enterococci in these infections remains controversial. The pathophysiological mechanisms induced by enterococci in intra-abdominal infection were studied in a nonfatal model of peritonitis in rats by implanting a gelatin capsule containing Escherichia coli and Bacteroides fragilis with or without increasing concentrations of Enterococcus faecalis or heat-inactivated enterococci. The ability of the rat peritoneal cavity to sterilize itself after bacterial challenge was evaluated by quantifying the inflammatory response in the peritoneal cavity, reflected by both phagocyte and cytokine responses. Effects were evaluated 6, 12, and 24 h and 3 and 6 days after inoculation. On day 6 after inoculation, the highest enterococcal concentration (10(8) CFU/ml) was accompanied by significantly increased concentrations of E. coli in peritoneal fluid and peritoneal phagocytes when compared to other groups. In the first 12 h after inoculation, tumor necrosis factor and interleukin-6 concentrations were significantly increased in the peritoneal fluid of the animals that had received the highest inoculum of enterococci or heat-inactivated enterococci. In the late period of the study (3 and 6 days), significantly increased leukocyte counts were observed in the peritoneal fluid of these animals. These results suggest that E. faecalis somehow inhibited phagocytosis and intracellular killing of the other pathogens and also played an inflammatory role, which might account for the bacterial synergy observed in this model.

Animals↗
PubMed1997

Enterococcus faecalis antigens in human infections.

Genomic libraries of two Enterococcus faecalis strains, OG1RF and TX52 (an isolate from an endocarditis patient), were constructed in cosmid vectors pBeloBAC11 and pLAFRx, and screened with a serum from a rabbit immunized with surface proteins of an E. faecalis endocarditis isolate and sera from four patients with enterococcal endocarditis. Seventy-five cosmid clones reacted with at least two of the sera. Thirty-eight of the 75 immunopositive clones were considered to contain distinct inserts based on their DNA restriction patterns and were chosen for further subcloning into a pBluescript vector. Each sublibrary was screened with one of the five sera, and the DNA sequence of the immunopositive subclones was determined. Analysis of these sequences revealed similarities to a range of proteins, including bacterial virulence factors, transporters, two-component regulators, metabolic enzymes, and membrane or cell surface proteins. Fourteen subclones did not show significant similarity to any sequence in the databases and may contain novel genes. Thirteen of the immunopositive cosmid clones did not yield immunopositive subclones, and one such cosmid clone produced a nonprotein antigen in Escherichia coli.

Antibodies, Bacterial↗
PubMed1998

Aggregation and binding substances enhance pathogenicity in rabbit models of Enterococcus faecalis endocarditis.

We investigated the importance of enterococcal aggregation substance (AS) and enterococcal binding substance (EBS) in rabbit models of Enterococcus faecalis cardiac infections. First, American Dutch belted rabbits were injected intraventricularly with 10(8) CFU and observed for 2 days. No clinical signs of illness developed in animals given AS- EBS- organisms, and all survived. All rabbits given AS- EBS+ organisms developed signs of illness, including significant pericardial inflammation, but only one of six died. All animals given AS+ EBS- organisms developed signs of illness, including pericardial inflammation, and survived. All rabbits given AS+ EBS+ organisms developed signs of illness and died. None of the rabbits receiving AS+ EBS+ organisms showed gross pericardial inflammation. The lethality and lack of inflammation are consistent with the presence of a superantigen. Rabbit and human lymphocytes were highly stimulated in vitro by cell extracts, but not cell-free culture fluids, of AS+ EBS+ organisms. In contrast, cell extracts from AS- EBS- organisms weakly stimulated lymphocyte proliferation. Culture fluids from human lymphocytes stimulated with AS+/EBS+ enterococci contained high levels of gamma interferon and tumor necrosis factor alpha (TNF-alpha) and TNF-beta, which is consistent with functional stimulation of T-lymphocyte proliferation and macrophage activation. Subsequent experiments examined the abilities of the same strains to cause endocarditis in a catheterization model. New Zealand White rabbits underwent transaortic catheterization for 2 h, at which time catheters were removed and animals were injected with 2 x 10(9) CFU of test organisms. None of the animals given AS- EBS- organisms developed vegetations or showed autopsy evidence of tissue damage. Rabbits given AS- EBS+ or AS+ EBS- organisms developed small vegetations and had splenomegaly at autopsy. All rabbits given AS+ EBS+ organisms developed large vegetations and had splenomegaly and lung congestion at autopsy. Similar experiments that left catheters in place for 3 days revealed that all rabbits given AS- EBS- or AS+ EBS+ organisms developed vegetations, but animals given AS+ EBS+ organisms had larger vegetations and autopsy evidence of lung congestion. These experiments provide direct evidence that these two cell wall components play an important role in the pathogenesis of endocarditis as well as in conjugative plasmid transfer.

Adhesins, Bacterial↗
PubMed1998

Molecular epidemiology of Staphylococcus aureus and Enterococcus faecalis in endophthalmitis.

Genomic DNA fingerprint analysis was performed on 39 Staphylococcus aureus and 28 Enterococcus faecalis endophthalmitis isolates collected from multiple clinical centers. Among 21 S. aureus genomic DNA fingerprint patterns identified, five clonotypes were recovered from multiple unrelated patients and accounted for 58.9% (23 of 39) of the isolates analyzed. Compared with strains having unique genomic DNA fingerprint patterns, the S. aureus clonotypes occurring more than once were more likely to result in visual acuities of 20/200 or worse (P = 0.036 [chi2 test]). In contrast to the S. aureus isolates, the E. faecalis endophthalmitis isolates were a clonally diverse population, enriched for the expression of a known toxin, cytolysin, which is plasmid encoded.

Bacterial Typing Techniques↗
PubMed1998

Enterococcus faecalis localization in experimental endophthalmitis: role of plasmid-encoded aggregation substance.

Enterococci have emerged as leading agents of nosocomial infection, yet relatively little is known about the pathogenesis of enterococcal disease. In previous studies, we developed an Enterococcus faecalis endophthalmitis infection model which provides unique opportunities to study the evolution of enterococcal disease by direct observation, as well as through sensitive electrophysiologic measures of organ function. The present study was designed to determine whether E. faecalis possesses traits that permit its attachment to mammalian tissues during infection. It was also of interest to determine whether a plasmid-encoded adhesin, aggregation substance, contributes to enterococcal localization or otherwise mediates adherence to alternate sites. These studies found that, in this model, enterococci attach to membranous structures occurring within the vitreous but that this attachment or the course or severity of disease is unaffected by the aggregation substance phenotype.

Adhesins, Bacterial↗
PubMed1998

Disparate findings on the role of virulence factors of Enterococcus faecalis in mouse and rat models of peritonitis.

The role of Enterococcus faecalis in polymicrobial peritonitis is still debated. Virulence factors expressed in some enterococcal strains might be involved in the pathogenicity of these organisms. To clarify their role, three of these virulence factors (cytolysin, gelatinase, and aggregation substance) were studied in six isogenic strains of E. faecalis expressing various combinations of these factors. Since the pathogenic effects of enterococci are only moderate, the expression of their virulence might vary from one animal species to another and from one type of infection to another. Therefore, we evaluated these effects in two animal models, i.e., a systemic infection in mice in which we assessed the virulence of the strains in 50% lethal dose studies and a model of compartmentalized infection in rats in which the microbiologic and inflammatory effects of the strains were evaluated in monomicrobial or polymicrobial infection. In mice, significant differences were observed in the cumulative survival curves depending on the virulence factors (P < 0.0001 [log rank test]). In rats, monomicrobial infection induced only mild changes. In polymicrobial peritonitis, the virulence factors mainly increased the inflammatory response while the changes observed in the microbiologic response were minimal. The combination of two virulence factors did not significantly increase the severity of infection either in the mice model or the polymicrobial rat model. These data argue for species and model dependence of the role of the virulence factors studied here and suggest that other important factors may be involved in the pathogenicity of enterococci.

Animals↗
PubMed1998

A cluster of genes involved in polysaccharide biosynthesis from Enterococcus faecalis OG1RF.

Our previous work identified a cosmid clone containing a 43-kb insert from Enterococcus faecalis OG1RF that produced a nonprotein antigen in Escherichia coli. In the present work, we studied this clone in detail. Periodate treatment of lysates of the clone confirmed that the antigen was carbohydrate in nature. Analysis of DNA sequences and transposon insertion mutants suggested that the insert contained a multicistronic gene cluster. Database comparison showed that the cluster contained genes similar to genes involved in the biosynthesis of dTDP-rhamnose, glycosyltransferases, and ABC transporters involved in the export of sugar polymers from both gram-positive and gram-negative organisms. Insertions in several genes within the cluster abolished the immunoreactivity of the clone. This is the first report on a gene cluster of E. faecalis involved in the biosynthesis of an antigenic polysaccharide.

Antigens, Bacterial↗
PubMed1999

Infection-derived Enterococcus faecalis strains are enriched in esp, a gene encoding a novel surface protein.

We report the identification of a new cell wall-associated protein of Enterococcus faecalis. Studies on the distribution of the gene encoding this novel surface protein, Esp, reveal a significant (P < 0.001) enrichment in infection-derived E. faecalis isolates. Interestingly, the esp gene was not identified in any of 34 clinical E. faecium isolates or in 4 other less pathogenic enterococcal species tested. Analysis of the structural gene among various E. faecalis isolates reveals the existence of alternate forms of expression of the Esp protein. The deduced primary structure of the Esp protein from strain MMH594, inferred to be 1,873 amino acids (aa) with a predicted mass of approximately 202 kDa, reveals a core region consisting of repeat units that make up 50% of the protein. Esp bears global organizational similarity to the Rib and C alpha proteins of group B streptococci. Identity among Esp, Rib, and C alpha proteins is strikingly localized to a stretch of 13 aa within repeats of similar length. The high degree of conservation of this 13-residue sequence suggests that it plays an important role in the natural selection for this trait among infection-derived E. faecalis and group B streptococcal isolates.

Adolescent↗
PubMed1999

Enterococcus faecalis bearing aggregation substance is resistant to killing by human neutrophils despite phagocytosis and neutrophil activation.

Enterococcus faecalis aggregation substance (AS) mediates efficient bacterium-bacterium contact to facilitate plasmid exchange as part of a bacterial sex pheromone system. We have previously determined that AS promotes direct, opsonin-independent binding of E. faecalis to human neutrophils (PMNs) via complement receptor type 3 and other receptors on the PMN surface. We have now examined the functional consequences of this bacterium-host cell interaction. AS-bearing E. faecalis was phagocytosed and internalized by PMNs, as determined by deconvolution fluorescence microscopy. However, these bacteria were not killed by PMNs, and internalized bacteria excluded propidium iodide, indicating intact bacterial membranes. Resistance to killing occurred despite activation of PMNs, as indicated by an increase in both functional and total surface Mac-1 expression, shedding of L-selectin, and an increase in PMN extracellular superoxide and phagosomal oxidant production. Deconvolution fluorescence microscopy also revealed that phagosomes containing AS-bearing bacteria were markedly larger than phagosomes containing opsonized E. faecalis, suggesting that some modification of phagosomal maturation may be involved in AS-induced resistance to killing. PMN phagosomal pH was significantly higher after ingestion of nonopsonized AS-bearing E. faecalis than after that of opsonized bacteria. The novel ability of AS to promote intracellular survival of E. faecalis inside PMNs suggests that AS may be a virulence factor used by strains of E. faecalis.

Animals↗
PubMed1999

Isolation of Enterococcus faecalis clinical isolates that efficiently adhere to human bladder carcinoma T24 cells and inhibition of adhesion by fibronectin and trypsin treatment.

The adherence of Enterococcus faecalis strains to human T24 cells was examined by scanning electron microscopy. Five highly adhesive strains were identified from 30 strains isolated from the urine of patients with urinary tract infections. No efficiently adhesive strains were found among the 30 strains isolated from the feces of healthy students. The five isolated strains also adhered efficiently to human bladder epithelial cells. Analysis of restriction endonuclease-digested plasmid DNAs and chromosome DNAs showed that the five strains were different strains isolated from different patients. The adhesiveness of these strains was inhibited by treatment with fibronectin or trypsin, implying that a specific protein (adhesin) on the bacterial cell surface mediates adherence to fibronectin on the host cell surfaces, and the adhesin differs from the reported adhesins.

Bacterial Adhesion↗
PubMed1999

Humoral immunity to commensal oral bacteria in human infants: salivary secretory immunoglobulin A antibodies reactive with Streptococcus mitis biovar 1, Streptococcus oralis, Streptococcus mutans, and Enterococcus faecalis during the first two years of life.

Secretory immunoglobulin A (SIgA) antibodies reactive with the pioneer oral streptococci Streptococcus mitis biovar 1 and Streptococcus oralis, the late oral colonizer Streptococcus mutans, and the pioneer enteric bacterium Enterococcus faecalis in saliva samples from 10 human infants from birth to age 2 years were analyzed. Low levels of salivary SIgA1 and SIgA2 antibodies reactive with whole cells of all four species were detected within the first month after birth, even though S. mutans and E. faecalis were not recovered from the mouths of the infants during the study period. Although there was a fivefold increase in the concentration of SIgA between birth and age 2 years, there were no differences between the concentrations of SIgA1 and SIgA2 antibodies reactive with the four species over this time period. When the concentrations of SIgA1 and SIgA2 antibodies reactive with all four species were normalized to the concentrations of SIgA1 and SIgA2 in saliva, SIgA1 and SIgA2 antibodies reactive with these bacteria showed a significant decrease from birth to 2 years of age. Adsorption of each infant's saliva with cells of one species produced a dramatic reduction of antibodies recognizing the other three species. Sequential adsorption of saliva samples removed all SIgA antibody to the bacteria, indicating that the SIgA antibodies were directed to antigens shared by all four species. The induction by the host of a limited immune response to common antigens that are likely not involved in adherence may be among the mechanisms that commensal streptococci employ to persist in the oral cavity.

Antibodies, Bacterial↗
PubMed1999

Survival of Enterococcus faecalis in mouse peritoneal macrophages.

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 DH5alpha 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 DH5alpha 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 internalized E. coli DH5alpha decreased 20, 542-fold. The difference in the rate of survival of E. faecalis strains and E. coli DH5alpha 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. faecalis strains 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. faecalis can persist for an extended period in mouse peritoneal macrophages.

Animals↗
PubMed1999

A novel means of self-protection, unrelated to toxin activation, confers immunity to the bactericidal effects of the Enterococcus faecalis cytolysin.

Enterococcus faecalis has become a pervasive clinical problem due to the emergence of resistance to most antibiotics. The cytolysin of E. faecalis is a novel bacterial toxin that contributes to the severity of disease. It consists of two structural subunits, which together possess both hemolytic and bactericidal activity. Both toxin subunits are encoded in a complex operon frequently harbored on pheromone-responsive plasmids. E. faecalis strains lacking such plasmids are susceptible to the bactericidal effects of the cytolysin. A novel cytolysin immunity determinant at the 3' end of the pAD1 cytolysin operon is described in the present study. Deletion analysis and specific mutagenesis isolated the immunity function to a single open reading frame. Specific mutagenesis experiments demonstrate that cytolysin immunity is unrelated to cytolysin activator (CylA) expression as previously proposed. Cytolysin immunity is, however, encoded on the same transcript as and 3' to CylA, and previous associations between immunity and CylA can be ascribed to the polar behavior of Tn917 insertion.

Amino Acid Sequence↗
PubMed2000

Inducible expression of Enterococcus faecalis aggregation substance surface protein facilitates bacterial internalization by cultured enterocytes.

Aggregation substance (AS) is an Enterococcus faecalis surface protein that may contribute to virulence. Using a recently described system for controlled expression of AS in E. faecalis and the heterologous host Lactococcus lactis, experiments were designed to assess the effect of AS on bacterial internalization by HT-29 and Caco-2 enterocytes. AS expression was associated with increased internalization of E. faecalis by HT-29 enterocytes and of L. lactis by HT-29 and Caco-2 enterocytes. Compared to enterocytes cultivated under standard conditions, either cultivation in hypoxia or 1-h pretreatment of enterocytes with calcium-free medium resulted in increased internalization of both E. faecalis and L. lactis (with and without AS expression). Also, AS expression augmented these increases when E. faecalis was incubated with pretreated HT-29 enterocytes and when L. lactis was incubated with pretreated Caco-2 and HT-29 enterocytes. These data indicated that AS might facilitate E. faecalis internalization by cultured enterocytes.

Bacterial Proteins↗