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PubMed1999

The osmoprotectant glycine betaine inhibits salt-induced cross-tolerance towards lethal treatment in Enterococcus faecalis.

The response of Enterococcus faecalis ATCC 19433 to salt stress has been characterized previously in complex media. In this report, it has been demonstrated that this bacterium actively accumulates the osmoprotectant glycine betaine (GB) from salt-enriched complex medium BHI. To further understand the specific effects of GB and other osmoprotective compounds in salt adaptation and salt-induced cross-tolerance to lethal challenges, a chemically defined medium lacking putative osmoprotectants was used. In this medium, bacterial growth was significantly reduced by increasing concentrations of NaCl. At 0.75 M NaCl, 90% inhibition of the growth rate was observed; GB and its structural analogues restored growth to the non-salt-stressed level. In contrast, proline, pipecolate and ectoine did not allow growth recovery of stressed cells. Kinetic studies showed that the uptake of betaines shows strong structural specificity and occurs through a salt-stress-inducible high-affinity porter [Km = 3.3 microM; Vmax = 130 nmol min(-1) (mg protein)(-1); the uptake activity increased 400-fold in the presence of 0.5 M NaCl]. Moreover, GB and its analogues were accumulated as non-metabolizable cytosolic osmolytes and reached intracellular levels ranging from 1-3 to 1.5 micromol (mg protein)(-1). In contrast to the beneficial effect of GB on the growth of salt-stressed cultures of E. faecalis, its accumulation inhibits the salt-induced cross-tolerance to a heterologous lethal challenge. Indeed, pretreatment of bacterial cells with 0.5 M NaCl induced resistance to 0.3% bile salts (survival of adapted cells increased by a factor of 6800). The presence of GB in the adaptation medium reduced the acquisition of bile salts resistance 680-fold. The synthesis of 11 of the 13 proteins induced during salt adaptation was significantly reduced in the presence of GB. These results raise questions about the actual beneficial effect of GB in natural environments where bacteria are often subjected to various stresses.

Adaptation, Physiological↗

PubMed2005

Silencing of glycopeptide resistance in Enterococcus faecalis BM4405 by novobiocin.

Enterococcus faecalis BM4405-1, a susceptible derivative of the VanE-type vancomycin-resistant E. faecalis strain BM4405, was obtained after growth in the presence of novobiocin, an inhibitor of the GyrB subunit of DNA gyrase. In contrast to findings for BM4405, UDP-MurNAc-L-Ala-gamma-D-Glu-L-Lys-D-Ala-D-Ala (pentapeptide[D-Ala]) was the only peptidoglycan precursor found in BM4405-1, and no VanXY(E) D,D-peptidase or VanT serine racemase activities were detected in that strain, even after induction by subinhibitory concentrations of vancomycin. Sequencing of the vanE operon of BM4405-1 revealed two mutations leading to substitutions in VanE (D200N) and in the C-terminal amino acid of VanR(E) (Y225F). Cloning of the vanE, vanXY(E), and vanT(E) genes of BM4405-1 into the susceptible E. faecalis strain JH2-2 conferred resistance to vancomycin, indicating that the mutation in vanE was not responsible for susceptibility. Transcriptional analysis of the vanE operon in BM4405 by quantitative reverse transcription-PCR indicated that novobiocin did not affect the expression level of the vanE operon. Sequencing of the gyrB gene of BM4405-1 revealed a mutation responsible for substitution of a residue (K337Y) required for ATPase activity and thus implicated in DNA supercoiling. Cloning of the gyrB gene of BM4405 restored vancomycin resistance to BM4405-1. Taken together, these data suggest that alteration of DNA supercoiling following a mutation in GyrB was responsible for lack of expression of the vanE operon and thus for vancomycin susceptibility in BM4405-1.

Anti-Bacterial Agents↗

PubMed2005

Specific control of endogenous cCF10 pheromone by a conserved domain of the pCF10-encoded regulatory protein PrgY in Enterococcus faecalis.

Conjugative transfer of Enterococcus faecalis plasmid pCF10 is induced by the heptapeptide pheromone cCF10. cCF10 produced by plasmid-free recipient cells is detected by pCF10-containing donor cells, which respond by induction of plasmid-encoded transfer functions. The pCF10-encoded membrane protein PrgY is essential to prevent donor cells from responding to endogenously produced pheromone while maintaining the ability to respond to pheromone from an exogenous source; this function has not been identified in any nonenterococcal prokaryotic signaling system. PrgY specifically inhibited endogenous cCF10 and cPD1 (a pheromone that induces transfer of closely related plasmid pPD1) but not cAD1 (which is specific for less-related plasmid pAD1). Ectopic expression of PrgY in plasmid-free recipient cells reduced pheromone activity in culture supernatants and reduced the ability of these cells to acquire pCF10 by conjugation but did not have any effect on the interaction of these cells with exogenously supplied cCF10. The cloned prgY gene could complement a pCF10 prgY null mutation, and complementation was used to identify point mutations impairing PrgY function. Such mutations also abolished the inhibitory effect of PrgY expression in recipients on pheromone production and on acquisition of pCF10. Most randomly generated point mutations identified in the genetic screen mapped to a predicted extracellular domain in the N terminus of PrgY that is conserved in a newly identified family of related proteins from disparate species including Borrelia burgdorferi, Archaeoglobus fulgidus, Arabidopsis thaliana, and Homo sapiens. The combined genetic and physiological data suggest that PrgY may sequester or inactivate cCF10 as it is released from the membrane.

Amino Acid Sequence↗

PubMedDate not supplied

Enterococcus faecalis endocarditis presenting as meningitis.

Although Enterococcus faecalis is a relatively common cause of infective endocarditis, it rarely causes meningitis. A case of Enterococcus faecalis endocarditis presenting as meningitis in a 74-year-old diabetic man on chronic hemodialysis is reported. A review of the literature showed that the association of enterococcal meningitis and endocarditis has rarely been reported. This clinical association may be more common than previously recognized and it is suggested that echocardiography be considered for all patients with enterococcal hematogenous meningitis in order to rule out endocarditis.

Endocarditis, Bacterial↗

PubMed1997

Subdural empyema due to Enterococcus faecalis.

Central nervous system infections due to Enterococcus species are uncommon. We report the first case of subdural empyema due to Enterococcus faecalis. Following partial treatment of a middle ear infection due to Enterococcus species and mixed coliforms, the patient developed signs of meningeal involvement. A lumbar puncture showed a raised polymorph cell count, but was sterile on culture; broad-spectrum antimicrobial therapy with cefotaxime, flucloxacillin and metronidazole was commenced. Following development of focal neurological signs, a CT scan revealed a subdural collection. Drainage and culture of the pus yielded a pure growth of Enterococcus faecalis. This case demonstrates the need to remain aware of the ability of the Enterococcus to cause serious infections and to direct specific antimicrobial therapy accordingly.

Adolescent↗

PubMed1997

In-vitro studies of the activity of glycopeptide combinations against Enterococcus faecalis biofilms.

Perfused biofilms of Enterococcus faecalis reached a pseudo-steady state, with respect to bioburden and the numbers of cells liberated within the perfusates. Biofilm growth rate was slow (approximately 0.006 doublings/h) relative to batch culture (approximately 0.01 doublings/h). MICs were determined for vancomycin (0.12 mg/L) and teicoplanin (1.2 mg/L) in batch culture. Steady-state biofilms (24 h and 48 h) were perfused continuously for 96 h with medium containing antibiotic at 4 X MIC. Susceptibility was assessed as cfu in the perfusate, indicating growth inhibition, and as cfu for the parent biofilm. Vancomycin at these levels had little or no effect on either parameter, whilst teicoplanin produced a temporary (30 h) reduction in growth rate (99.99% for 24 h biofilms, 50% for 48 h biofilms). Antibiotic concentrations were raised to therapeutic (trough) levels (vancomycin, 5 mg/L; teicoplanin, 12 mg/L) and applied continuously to 24 h old biofilms. Neither agent affected viability of the biofilm over 96 h. Biofilm growth rate, however, was decreased markedly over the first 8-10 h of antibiotic treatment and was maintained at the reduced level for approximately 40 h. Thereafter growth of the biofilms gradually returned to pre-exposure levels. The pattern of recovery was different for the two agents suggesting that different mechanisms might be involved. Accordingly biofilms were exposed to successive and concurrent 24 h treatments with vancomycin (5 mg/L) and teicoplanin (12 mg/L). This led not only to a further 2-3 log reduction in the growth rate but also to a 3 log reduction in the viability of the parent biofilm. Such synergy between the glycopeptide agents might have therapeutic implications for the treatment of E. faecalis infection.

Anti-Bacterial Agents↗

PubMed2001

Pulmonary hypertension syndrome in broilers caused by Enterococcus faecalis.

A field strain of Enterococcus faecalis was administered to broiler chicks at doses of 0, 3 x 10(6), 1.5 x 10(7), and 2 x 10(7) bacteria/bird either intra-abdominally or intravenously. In trials 1 to 3, birds were reared communally in a broiler house on pine shaving litter. In trial 4, challenged and control birds were maintained in separate isolation rooms in metal cages with raised wire floors. Challenged birds exhibited a characteristic cavity or depression in the external wall of the right ventricle. A subjective scoring system was devised to quantify challenge effects by assigning each heart a score of 1 to 4. The average number of birds, over all trials and over all dose levels, exhibiting the ventricular cavity was 93%. This value in controls was 5%. The average heart score for challenged birds was 3.1, and that for controls was 0.20. Heart scores of challenged and control chicks were not different in birds reared communally or in separate isolation rooms. Additionally, both routes of administration were equally effective. Results suggest that challenge with E. faecalis caused pulmonary hypertension.

Animals↗

PubMed2002

Enterococcus faecalis heme-dependent catalase.

Enterococcus faecalis cells cannot synthesize porphyrins and do not rely on heme for growth but can take up heme and use it to synthesize heme proteins. We recently described a cytochrome bd in E. faecalis strain V583 and here report the identification of a chromosomal gene, katA, encoding a heme-containing cytoplasmic catalase. The 54-kDa KatA polypeptide shows sequence similarity to members of the family of monofunctional catalases. A hexahistidyl-tagged version of the catalase was purified, and major characteristics of the enzyme were determined. It contains one protoheme IX group per KatA polypeptide. Catalase activity was detected only in E. faecalis cells grown in the presence of heme in the medium; about 2 and 10 micro M hemin was required for half-maximal and maximal production of catalase, respectively. Our finding of a catalase whose synthesis is dependent on the acquisition of heme in the opportunistic pathogen E. faecalis might be of clinical importance. Studies of cellular heme transport and heme protein assembly and in vivo synthesis of metalloprotein analogs for biotechnological applications are impeded by the lack of experimental systems. We conclude that the E. faecalis cell potentially provides such a desired system.

Bacillus subtilis↗

PubMed1995

Purification of sex pheromones specific for pMB1 and pMB2 plasmids of Enterococcus faecalis S-48.

The strain Enterococcus faecalis S-48 carries two large conjugative plasmids (pMB1 and pMB2) encoding for antagonistic substances. The pheromone response of these two plasmids was established by purifying the corresponding sex pheromones, using conventional reversed-phase columns. Plasmid pMB1 responds to pheromone cCF10. Plasmid pMB2 responds to a pheromone with an amino acid sequence identical to that of cPD1 (Phe-Leu-Val-Met-Phe-Leu-Ser-Gly). The two pheromone-responding plasmids coexist in a stable fashion in the wild-type strain E. faecalis S-48.

Amino Acid Sequence↗

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↗

PubMed2005

[Inhibition of hemolytic activity of Staphylococcus aureus 3-hemolysin by an exosubstance produced by some Enterococcus faecalis strains].

OBJECTIVE: Accidentally, some Enterococcus faecalis strains were found to inhibit the hemolysis caused by Staphylococcus aureus beta-hemolysin. The study objectives were to define the conditions under which this phenomenon appears and to characterize the inhibitory agent. MATERIALS AND METHODS: Ninety-one wild strains and five type strains of E. faecalis and nine wild E. faecium strains were tested for antihemolytic activity on blood agar with 5% sheep erythrocytes prepared using the following agar bases: Columbia Agar Base (BBL, 211124), Columbia Agar (Bio Mérieux, 51026), Blood Agar Base (Bio-Rad, 64524), Blood Agar Base (Columbia) (Ferosa, 1-034), Columbia Blood Agar Base (HiMedia, M114), Blood Agar Base No. 4 (Imuna), Columbia Agar Base (Merck, 10455) and Columbia Agar Base (Oxoid, CM331). The exosubstance produced by E. faecalis strains was isolated by means of acetone precipitation and was exposed to elevated temperature and trypsin. RESULTS: Thirty-three (36%) out of 91 wild strains of E. faecalis produced the substance inhibiting hemolysis caused by Staphylococcus aureus beta-hemolysin. Two out of five E. faecalis type strains and none of E. faecium strains appeared to be producers of the same substance. Inhibition of the hemolysis was observed on all of the media tested, being the most pronounced with the use of Blood Agar Base No. 4 (Imuna) and Columbia Agar Base (BBL) at pH 7.0-7.5 when cultured at 37 degrees C for 24 hours. The exosubstance lost its inhibitory effect after exposure to 70 degrees C for 15 min and to 0.1% trypsin for 30 min. The inhibitory potential against staphylococcal hemolysis correlated with the ability of strains to produce protease. CONCLUSION: About one third of wild E. faecalis strains produce a protease-like substance that seems proteinaceous in nature and has an inhibitory effect on the hemolysis caused by Staphylococcus aureus beta-hemolysin.

Animals↗

PubMed2000

Characterization and analysis of a new gene involved in glucose starvation response in Enterococcus faecalis.

The genome sequence of Enterococcus faecalis, led us to discover that gls24, encoding a general stress protein, seems to be in the second last position of a putative six-gene operon structure. Interestingly, another gene named orf4 located just upstream from gls24 shows strong identity (72%) with this last. To determine the role of the orf4 gene in E. faecalis, we have constructed a mutant strain by homologous recombination. Phenotypic analysis of these cells, reveals that Orf4 is probably involved in cell structure in stationary phase.

Enterococcus faecalis↗

PubMed1989

In vitro susceptibility studies of vancomycin-resistant Enterococcus faecalis.

Vancomycin resistance exhibited by Enterococcus faecalis isolates V583, V586, and V587 is described. The vancomycin MICs ranged from 32 to 64 micrograms/ml. Although resistant to vancomycin, the isolates were susceptible to teicoplanin (MIC, less than or equal to 0.5 micrograms/ml). Such a glycopeptide susceptibility profile has not been previously described for E. faecalis. Time kill studies showed that vancomycin resistance adversely affected the synergistic activity that vancomycin and aminoglycoside combinations usually demonstrate against enterococci. However, the ability to detect vancomycin resistance varied with the susceptibility testing method used. Whereas broth microdilution, broth macrodilution, and agar dilution methods detected resistance, disk-agar diffusion and the AutoMicrobic system Gram-Positive GPS-A susceptibility card (Vitek Systems Inc., Hazelwood, Mo.) did not. To detect vancomycin resistance reliably and establish the incidence of such E. faecalis isolates, adjustments in some susceptibility testing methods may be necessary.

Anti-Bacterial Agents↗

PubMed2000

Oxalate-degrading Enterococcus faecalis.

An oxalate-degrading Enterococcus faecalis was isolated from human stools under anaerobic conditions. The bacteria required a poor nutritional environment and repeated subculturing to maintain their oxalate-degrading ability. The E. faecalis produced 3 proteins (65, 48, and 40 kDa) that were not produced by non-oxalate-degrading E. faecalis as examined by SDS-PAGE. Antibodies against oxalyl-coenzyme A decarboxylase (65 kDa) and formyl-coenzyme A transferase (48 kDa) obtained from Oxalobacter formigenes (an oxalate-degrading anaerobic bacterium in the human intestine) reacted with 2 of the proteins (65 and 48 kDa) from the E. faecalis as examined by Western blottings. This is the first report on the isolation of oxalate-degrading facultative anaerobic bacteria from humans.

Adult↗

PubMed2004

Molecular epidemiology of the fsr locus and of gelatinase production among different subsets of Enterococcus faecalis isolates.

We examined 215 Enterococcus faecalis isolates and found that neither the two-component regulatory locus fsr (E. faecalis regulator) nor gelatinase production was more common in disease-associated isolates than in isolates colonizing healthy individuals (ca. 60 to 65%). The majority of gelatinase-negative isolates, including 14 endocarditis isolates (of 80 isolates tested), contained the previously described 23.9-kb deletion and lacked fsrA and fsrB. While these findings indicate that neither fsr nor gelatinase is required for E. faecalis to cause infection, this study did not address whether fsr or gelatinase affects the severity of disease, as it does in animal models.

Base Sequence↗

PubMed2006

Endocarditis and biofilm-associated pili of Enterococcus faecalis.

Increasing multidrug resistance in Enterococcus faecalis, a nosocomial opportunist and common cause of bacterial endocarditis, emphasizes the need for alternative therapeutic approaches such as immunotherapy or immunoprophylaxis. In an earlier study, we demonstrated the presence of antibodies in E. faecalis endocarditis patient sera to recombinant forms of 9 E. faecalis cell wall-anchored proteins; of these, we have now characterized an in vivo-expressed locus of 3 genes and an associated sortase gene (encoding sortase C; SrtC). Here, using mutation analyses and complementation, we demonstrated that both the ebp (encoding endocarditis and biofilm-associated pili) operon and srtC are important for biofilm production of E. faecalis strain OG1RF. In addition, immunogold electron microscopy using antisera against EbpA-EbpC proteins as well as patient serum demonstrated that E. faecalis produces pleomorphic surface pili. Assembly of pili and their cell wall attachment appeared to occur via a mechanism of cross-linking of the Ebp proteins by the designated SrtC. Importantly, a nonpiliated, allelic replacement mutant was significantly attenuated in an endocarditis model. These biologically important surface pili, which are antigenic in humans during endocarditis and encoded by a ubiquitous E. faecalis operon, may be a useful immunotarget for studies aimed at prevention and/or treatment of this pathogen.

Aminoacyltransferases↗

PubMed2002

ccfA, the genetic determinant for the cCF10 peptide pheromone in Enterococcus faecalis OG1RF.

The nosocomial pathogen Enterococcus faecalis has a unique pheromone-inducible conjugative mating system. Conjugative transfer of the E. faecalis plasmid pCF10 is specifically induced by the cCF10 peptide pheromone (LVTLVFV). Genomic sequence information has recently allowed the identification of putative structural genes coding for the various enterococcal pheromones (D. B. Clewell et al., Mol. Microbiol. 35:246-247, 2000). The cCF10 pheromone sequence LVTLVFV was found within an open reading frame designated ccfA, encoding a putative lipoprotein precursor. Several other pheromone sequences were found in similar locations within other predicted lipoproteins. CcfA shows significant sequence relatedness to the Escherichia coli protein YidC, an inner membrane protein translocase, as well as to a large number of homologs identified in gram-positive and in gram-negative bacteria. Analysis of the deduced CcfA amino acid sequence suggested that mature cCF10 peptide could be formed from the proteolytic degradation of its signal peptide. Expression of the cloned ccfA gene with an inducible expression vector dramatically increased cCF10 production by E. faecalis and also resulted in cCF10 production by Lactococcus lactis, a non-pheromone producer. Site-directed mutagenesis of the ccfA sequence encoding the cCF10 peptide confirmed that ccfA was a functional genetic determinant for cCF10.

Amino Acid Sequence↗

PubMed2004

Inhibition of Listeria monocytogenes by enterocin EJ97 produced by Enterococcus faecalis EJ97.

Enterocin EJ97 from Enterococcus faecalis EJ97 showed a concentration-dependent antimicrobial activity against Listeria monocytogenes CECT 4032. Activity of enterocin EJ97 against L. monocytogenes CECT 4032 increased slightly at 4 degrees C, and cold-adapted cells did not show any increased resistance. Sensitivity of L. monocytogenes CECT 4032 to enterocin EJ97 was not modified by the addition of sodium benzoate, sodium acetate, NaCl or sodium tripolyphosphate. Anti-listeria activity was enhanced by potassium nitrate, and especially by sodium nitrite at concentrations of 50 microg/ml or above. E. faecalis EJ97 produced bacteriocin activity during cocultivation with L. monocytogenes CECT 4032 at 37 degrees C and also at 15 degrees C, but not at 4 degrees C. Growth of L. monocytogenes CECT 4032 was inhibited by bacteriocin produced during cocultivation at 37 and 15 degrees C, and the degree of inhibition was influenced by the incubation temperature and the initial concentrations of enterococci and listeria. E. faecalis EJ97 also produced bacteriocin during cocultivation in half-skimmed milk, although its capacity to control L. monocytogenes was limited to populations of 10(3) CFU/ml or lower.

Animals↗